[Solved]-remove grid line on chart-Highcharts

for all other lines here is what worked for me, in some cases using line transparency as the color was the only solution I could find.

$(function() {                                                                                                                                               
  $('#container').highcharts({                                                                                                                               
    colors: ['#00f900', '#ffff3c', '#ff2600'],                                                                                                               
    credits: {                                                                                                                                               
      enabled: false                                                                                                                                         
    },                                                                                                                                                       
    exporting: {                                                                                                                                             
      enabled: false                                                                                                                                         
    },                                                                                                                                                       
    legend: {                                                                                                                                                
      itemDistance: 60                                                                                                                                       
    },                                                                                                                                                       
    lineColor: 'red',                                                                                                                                        
    chart: {                                                                                                                                                 
      type: 'column',                                                                                                                                        
      backgroundColor: 'transparent'                                                                                                                         
    },                                                                                                                                                       
    title: {                                                                                                                                                 
      text: ''                                                                                                                                               
    },                                                                                                                                                       
    legend: {                                                                                                                                                
      itemStyle: {                                                                                                                                           
        color: 'white',                                                                                                                                      
        fontWeight: 'normal',                                                                                                                                
        fontFamily: 'helvetica',                                                                                                                             
        fontSize: '12px'                                                                                                                                     
      }                                                                                                                                                      
    }
// ....rest in js fiddle

http://jsfiddle.net/fv50sLkj/23/

you just need to gridLineWidth set to 0
yAxis: {
           min:0,
           categories: ["","Low","Medium","High"],
           tickWidth: 0,
           crosshair: false,
           lineWidth: 0,
           gridLineWidth:0,//Set this to zero
           title: '',
           labels: {
                       formatter: function () {
                           return this.value;labels
                           }            
                       },
                       showEmpty: false
}

None of the mentioned solutions worked for me, so this one finally worked (taken from Sparklines examples: https://www.highcharts.com/demo/sparkline):

yAxis: {
    startOnTick: false,
    endOnTick: false,
    tickPositions: [],
}

If you doesn't want to touch the config object, you just hide the grid by css:

.chart-container .highcharts-grid {
   display: none;
}