Remove pages_use_legacy_storage_lease FF

We already tested it once in production and saw no problems

app/services/pages/legacy_storage_lease.rb

@@ -8,15 +8,6 @@ module Pages
 
     LEASE_TIMEOUT = 1.hour
 
-    # override method from exclusive lease guard to guard it by feature flag
-    # TODO: just remove this method after testing this in production
-    # https://gitlab.com/gitlab-org/gitlab/-/issues/282464
-    def try_obtain_lease
-      return yield unless Feature.enabled?(:pages_use_legacy_storage_lease, project, default_enabled: true)
-
-      super
-    end
-
     def lease_key
       "pages_legacy_storage:#{project.id}"
     end

config/feature_flags/development/pages_use_legacy_storage_lease.yml

----
-name: pages_use_legacy_storage_lease
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48349
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/282464
-milestone: '13.7'
-type: development
-group: group::release
-default_enabled: true

spec/services/pages/legacy_storage_lease_spec.rb

@@ -47,14 +47,6 @@ RSpec.describe ::Pages::LegacyStorageLease do
 
       expect(service.execute).to eq(nil)
     end
-
-    it 'runs guarded method if feature flag is disabled' do
-      stub_feature_flags(pages_use_legacy_storage_lease: false)
-
-      expect(service).to receive(:execute_unsafe).and_call_original
-
-      expect(service.execute).to eq(true)
-    end
   end
 
   context 'when another service holds the lease for the different project' do