Remove scanner alerts feature flag

This commit remvoes the `:scanner_alerts` feature flag and usage
from the codebase.

ee/app/assets/javascripts/security_dashboard/components/project_vulnerabilities.vue

@@ -2,7 +2,6 @@
 import produce from 'immer';
 import { GlAlert, GlLoadingIcon, GlIntersectionObserver } from '@gitlab/ui';
 import { __ } from '~/locale';
-import glFeatureFlagsMixin from '~/vue_shared/mixins/gl_feature_flags_mixin';
 import VulnerabilityList from './vulnerability_list.vue';
 import vulnerabilitiesQuery from '../graphql/project_vulnerabilities.graphql';
 import securityScannersQuery from '../graphql/project_security_scanners.graphql';
@@ -17,7 +16,6 @@ export default {
     GlIntersectionObserver,
     VulnerabilityList,
   },
-  mixins: [glFeatureFlagsMixin()],
   props: {
     projectFullPath: {
       type: String,
@@ -78,9 +76,6 @@ export default {
           pipelineRun: pipelineRun.map(translateScannerName),
         };
       },
-      skip() {
-        return !this.glFeatures.scannerAlerts;
-      },
     },
   },
   computed: {

ee/app/controllers/projects/security/dashboard_controller.rb

@@ -9,7 +9,6 @@ module Projects
 
       before_action only: [:index] do
         push_frontend_feature_flag(:hide_dismissed_vulnerabilities)
-        push_frontend_feature_flag(:scanner_alerts, default_enabled: true)
       end
     end
   end

ee/config/feature_flags/development/scanner_alerts.yml

----
-name: scanner_alerts
-introduced_by_url: 
-rollout_issue_url: 
-group: 
-type: development
-default_enabled: true