Delete the main_branch_over_master feature flag

This feature flag was introduced in 13.12, which is more than 4 milestones ago.

As part of our process we want to ensure feature flags don't stay too long in the codebase.

Rollout issue: #329190

Remaining mentions of the feature flag (click to expand)

ee/spec/factories/groups.rb
12:        stub_feature_flags(main_branch_over_master: false)

spec/factories/projects.rb
523:        stub_feature_flags(main_branch_over_master: false)

spec/lib/gitlab/default_branch_spec.rb
11:      stub_feature_flags(main_branch_over_master: true)

spec/services/design_management/save_designs_service_spec.rb
198:          stub_feature_flags(main_branch_over_master: true)

spec/spec_helper.rb
263:    stub_feature_flags(main_branch_over_master: false)
312:      stub_feature_flags(main_branch_over_master: false)

config/feature_flags/development/main_branch_over_master.yml
2:name: main_branch_over_master

ee/spec/factories/groups.rb
12:        stub_feature_flags(main_branch_over_master: false)

lib/gitlab/default_branch.rb
7:      Feature.enabled?(:main_branch_over_master, object) ? 'main' : 'master'

spec/factories/projects.rb
523:        stub_feature_flags(main_branch_over_master: false)

spec/lib/gitlab/default_branch_spec.rb
5:# We disabled main_branch_over_master feature for tests
9:  context 'main_branch_over_master is enabled' do
11:      stub_feature_flags(main_branch_over_master: true)
19:  context 'main_branch_over_master is disabled' do

spec/services/design_management/save_designs_service_spec.rb
198:          stub_feature_flags(main_branch_over_master: true)

spec/spec_helper.rb
263:    stub_feature_flags(main_branch_over_master: false)
308:      # Disable `main_branch_over_master` as we migrate
312:      stub_feature_flags(main_branch_over_master: false)

Currently the feature flag is enabled on production

It is possible that this MR will still need some changes to remove references to the feature flag in the code. At the moment the gitlab-housekeeper is not always capable of removing all references so you must check the diff and pipeline failures to confirm if there are any issues. It is the responsibility of groupsource code to push those changes to this branch.

Note: If you do not want to remove this feature flag at this time, you can add an intended_to_rollout_by_date attribute in the feature flag YAML file to prevent automated removal.

TODO for the reviewers before merging this MR

• See the status of the rollout by checking #329190, https://gitlab.com/gitlab-com/gl-infra/feature-flag-log/-/issues/?search=main_branch_over_master&sort=created_date&state=all&label_name%5B%5D=host%3A%3Agitlab.com
• Verify the feature flag status via chatops by running /chatops run feature get main_branch_over_master.
• Search for references to MainBranchOverMaster in frontend part of code
• Search for references to main_branch_over_master in code
• Check if we need to remove any Gem or other related code by looking at the changes in !60258 (merged)

This change was generated by gitlab-housekeeper in CI using the Keeps::DeleteOldFeatureFlags keep.

To provide feedback on your experience with gitlab-housekeeper please create an issue with the label GitLab Housekeeper and consider pinging the author of this keep.