Revert "Merge branch '55127-add-delay-after-mr-creation-for-async-tasks-to-complete' into 'master'"

This reverts merge request !27978

changelogs/unreleased/55127-add-delay-after-mr-creation-for-async-tasks-to-complete.yml

----
-title: Wait for pipeline creation to complete before accepting a MR via API
-merge_request: 27978
-author: kerrizor
-type: fixed

lib/api/merge_requests.rb

@@ -367,10 +367,6 @@ module API
         merge_request = find_project_merge_request(params[:merge_request_iid])
         merge_when_pipeline_succeeds = to_boolean(params[:merge_when_pipeline_succeeds])
 
-        if merge_when_pipeline_succeeds || merge_request.merge_when_pipeline_succeeds
-          render_api_error!('Not allowed: pipeline does not exist', 405) unless merge_request.head_pipeline
-        end
-
         # Merge request can not be merged
         # because user dont have permissions to push into target branch
         unauthorized! unless merge_request.can_be_merged_by?(current_user)

spec/requests/api/merge_requests_spec.rb

@@ -1495,33 +1495,6 @@ describe API::MergeRequests do
       expect(json_response['merge_when_pipeline_succeeds']).to eq(true)
     end
 
-    context 'when the MR requires pipeline success' do
-      it 'returns 405 if the pipeline is missing' do
-        allow_any_instance_of(MergeRequest)
-          .to receive(:merge_when_pipeline_succeeds).and_return(true)
-        allow_any_instance_of(MergeRequest).to receive(:head_pipeline).and_return(nil)
-
-        put api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/merge", user)
-
-        expect(response).to have_gitlab_http_status(405)
-        expect(json_response['message']).to eq('Not allowed: pipeline does not exist')
-      end
-    end
-
-    context 'when the request requires pipeline success' do
-      it 'returns 405 if the pipeline is missing' do
-        allow_any_instance_of(MergeRequest)
-          .to receive(:merge_when_pipeline_succeeds).and_return(true)
-        allow_any_instance_of(MergeRequest).to receive(:head_pipeline).and_return(nil)
-
-        put api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/merge", user),
-              params: { merge_when_pipeline_succeeds: true }
-
-        expect(response).to have_gitlab_http_status(405)
-        expect(json_response['message']).to eq('Not allowed: pipeline does not exist')
-      end
-    end
-
     it "returns 404 for an invalid merge request IID" do
       put api("/projects/#{project.id}/merge_requests/12345/merge", user)