Removed unused feature flag

config/feature_flags/development/webperf_experiment.yml

----
-name: webperf_experiment
-introduced_by_url: 
-rollout_issue_url: 
-milestone: 
-type: development
-group: group::editor
-default_enabled: false

lib/gitlab/gon_helper.rb

@@ -43,7 +43,6 @@ module Gitlab
 
       # Initialize gon.features with any flags that should be
       # made globally available to the frontend
-      push_frontend_feature_flag(:webperf_experiment, default_enabled: false)
       push_frontend_feature_flag(:snippets_binary_blob, default_enabled: false)
       push_frontend_feature_flag(:usage_data_api, default_enabled: true)
       push_frontend_feature_flag(:security_auto_fix, default_enabled: false)