Remove dataBackground property from chart

This commit removes the dataBackground property from the chart
options so that it behaves similar to the other charts on GitLab.

Changelog: changed

ee/app/assets/javascripts/security_dashboard/components/project/project_security_dashboard.vue

@@ -129,13 +129,6 @@ export default {
             type: 'slider',
             startValue: this.chartStartDate,
             handleIcon: this.svgs['scroll-handle'],
-            dataBackground: {
-              lineStyle: {
-                width: 1,
-                color: '#bfbfbf',
-              },
-              areaStyle: null,
-            },
           },
         ],
         toolbox: {

ee/spec/frontend/security_dashboard/components/project/project_security_dashboard_spec.js

@@ -119,10 +119,6 @@ describe('Project Security Dashboard component', () => {
         type: 'slider',
         handleIcon: 'path://mockSvgPathContent',
         startValue: '2021-03-12',
-        dataBackground: {
-          lineStyle: { width: 1 },
-          areaStyle: null,
-        },
       });
     });
   });