Remove post_import_repository_size_check ff

Changelog: added
EE: true

config/feature_flags/development/post_import_repository_size_check.yml

----
-name: post_import_repository_size_check
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122814
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/414530
-milestone: '16.1'
-type: development
-group: group::import and integrate
-default_enabled: false

ee/app/services/import/validate_repository_size_service.rb

@@ -7,8 +7,6 @@ def initialize(project)
     end
     def execute
-      return unless ::Feature.enabled?(:post_import_repository_size_check)
-
       project.repository.expire_content_cache
       ::Projects::UpdateStatisticsService.new(project, nil, statistics: [:repository_size]).execute

ee/spec/services/import/validate_repository_size_service_spec.rb

@@ -16,30 +16,20 @@
       end
     end
-    context 'when `post_import_repository_size_check` feature flag is enabled' do
-      context 'when repository size is over the limit' do
-        let(:above_size_limit) { true }
-        it 'schedules worker to destroy repository and raises error' do
-          expect(::Projects::RepositoryDestroyWorker).to receive(:perform_async).with(project.id)
-          expect { service.execute }
-            .to raise_error(::Projects::ImportService::Error, 'Repository above permitted size limit.')
-        end
-      end
-
-      context 'when repository size is not over the limit' do
-        let(:above_size_limit) { false }
-
-        it 'does nothing' do
-          expect(::Projects::RepositoryDestroyWorker).not_to receive(:perform_async)
-
-          expect(service.execute).to eq(nil)
-        end
+    context 'when repository size is over the limit' do
+      let(:above_size_limit) { true }
+      it 'schedules worker to destroy repository and raises error' do
+        expect(::Projects::RepositoryDestroyWorker).to receive(:perform_async).with(project.id)
+        expect { service.execute }
+          .to raise_error(::Projects::ImportService::Error, 'Repository above permitted size limit.')
       end
     end
-    context 'when `post_import_repository_size_check` feature flag is disabled' do
+    context 'when repository size is not over the limit' do
+      let(:above_size_limit) { false }
+
       it 'does nothing' do
         expect(::Projects::RepositoryDestroyWorker).not_to receive(:perform_async)