Remove the usage of `limit_projects_in_groups_api ` feature flag

This change removes the use of the
`limit_projects_in_groups_api` feature flag, which has been
enabled by default since 12.6

Changelog: other

config/feature_flags/development/limit_projects_in_groups_api.yml

----
-name: limit_projects_in_groups_api
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/20023
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/257829
-milestone: '12.6'
-type: development
-group: group::access
-default_enabled: true

lib/api/entities/group_detail.rb

@@ -29,11 +29,7 @@ module API
       end
 
       def projects_limit
-        if ::Feature.enabled?(:limit_projects_in_groups_api, default_enabled: true)
-          GroupProjectsFinder::DEFAULT_PROJECTS_LIMIT
-        else
-          nil
-        end
+        GroupProjectsFinder::DEFAULT_PROJECTS_LIMIT
       end
     end
   end

spec/requests/api/groups_spec.rb

@@ -631,30 +631,11 @@ RSpec.describe API::Groups do
         end
       end
 
-      context 'when limiting feature is enabled' do
-        before do
-          stub_feature_flags(limit_projects_in_groups_api: true)
-        end
-
-        it 'limits projects and shared_projects' do
-          get api("/groups/#{group1.id}")
-
-          expect(json_response['projects'].count).to eq(limit)
-          expect(json_response['shared_projects'].count).to eq(limit)
-        end
-      end
-
-      context 'when limiting feature is not enabled' do
-        before do
-          stub_feature_flags(limit_projects_in_groups_api: false)
-        end
-
-        it 'does not limit projects and shared_projects' do
-          get api("/groups/#{group1.id}")
+      it 'limits projects and shared_projects' do
+        get api("/groups/#{group1.id}")
 
-          expect(json_response['projects'].count).to eq(3)
-          expect(json_response['shared_projects'].count).to eq(3)
-        end
+        expect(json_response['projects'].count).to eq(limit)
+        expect(json_response['shared_projects'].count).to eq(limit)
       end
     end
   end