Remove usage_data_code_review_aggregation feature flag

MR: gitlab.com/gitlab-org/gitlab/-/merge_requests/64626

Changelog: other

config/feature_flags/development/usage_data_code_review_aggregation.yml

----
-name: usage_data_code_review_aggregation
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/53553
-rollout_issue_url: 
-milestone: '13.9'
-type: development
-group: group::code review
-default_enabled: true

config/metrics/aggregates/code_review.yml

@@ -9,7 +9,6 @@
 ---
 - name: code_review_group_monthly_active_users
   operator: OR
-  feature_flag: usage_data_code_review_aggregation
   source: redis
   time_frame: [7d, 28d]
   events:
@@ -68,7 +67,6 @@
     - 'i_code_review_user_resolve_conflict'
 - name: code_review_category_monthly_active_users
   operator: OR
-  feature_flag: usage_data_code_review_aggregation
   source: redis
   time_frame: [7d, 28d]
   events:
@@ -126,7 +124,6 @@
     - 'i_code_review_user_resolve_conflict'
 - name: code_review_extension_category_monthly_active_users
   operator: OR
-  feature_flag: usage_data_code_review_aggregation
   source: redis
   time_frame: [7d, 28d]
   events: