Remove feature flag usage_data_p_terraform_state_api_unique_users

Changelog: changed

config/feature_flags/development/usage_data_p_terraform_state_api_unique_users.yml

----
-name: usage_data_p_terraform_state_api_unique_users
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/50224
-rollout_issue_url:
-milestone: '13.8'
-type: development
-group: group::configure
-default_enabled: true

lib/gitlab/usage_data_counters/known_events/common.yml

@@ -344,7 +344,6 @@
   category: terraform
   redis_slot: terraform
   aggregation: weekly
-  feature_flag: usage_data_p_terraform_state_api_unique_users
 # Pipeline Authoring
 - name: o_pipeline_authoring_unique_users_committing_ciconfigfile
   category: pipeline_authoring

spec/requests/api/terraform/state_spec.rb

@@ -25,10 +25,6 @@ RSpec.describe API::Terraform::State do
     context 'without authentication' do
       let(:auth_header) { basic_auth_header('bad', 'token') }
 
-      before do
-        stub_feature_flags(usage_data_p_terraform_state_api_unique_users: false)
-      end
-
       it 'does not track unique event' do
         expect(Gitlab::UsageDataCounters::HLLRedisCounter).not_to receive(:track_event)