Remove undo endpoint

This reverts commit 2536fea8db0967a817615eb3e951eb6ba22f8ede.

app/controllers/projects/merge_requests_controller.rb

@@ -10,8 +10,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   before_action :module_enabled
   before_action :merge_request, only: [
     :edit, :update, :show, :diffs, :commits, :conflicts, :builds, :merge, :merge_check,
-    :ci_status, :toggle_subscription, :cancel_merge_when_build_succeeds, :remove_wip, :resolve_conflicts,
-    :undo_last_resolution
+    :ci_status, :toggle_subscription, :cancel_merge_when_build_succeeds, :remove_wip, :resolve_conflicts
   ]
   before_action :validates_merge_request, only: [:show, :diffs, :commits, :builds]
   before_action :define_show_vars, only: [:show, :diffs, :commits, :conflicts, :builds]
@@ -158,16 +157,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     end
   end
 
-  def undo_last_resolution
-    rugged = @merge_request.project.repository.rugged
-    ref = Gitlab::Git::BRANCH_REF_PREFIX + @merge_request.source_branch
-    prev = rugged.ref(ref).target
-
-    rugged.references.update(ref, prev.parents.first.oid) if prev.parents.length == 2
-
-    head :ok
-  end
-
   def builds
     respond_to do |format|
       format.html do

config/routes.rb

@@ -729,7 +729,6 @@ Rails.application.routes.draw do
             post :remove_wip
             get :diff_for_path
             post :resolve_conflicts
-            post :undo_last_resolution
           end
 
           collection do

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -639,19 +639,6 @@ describe Projects::MergeRequestsController do
       it 'returns an OK resposne' do
         expect(response).to have_http_status(:ok)
       end
-
-      context 'undoing the resolution' do
-        before do
-          post :undo_last_resolution,
-               namespace_id: merge_request_with_conflicts.project.namespace.to_param,
-               project_id: merge_request_with_conflicts.project.to_param,
-               id: merge_request_with_conflicts.iid
-        end
-
-        it 'undoes the commit' do
-          expect(original_head_sha).to eq(merge_request_with_conflicts.source_branch_head.sha)
-        end
-      end
     end
 
     context 'when sections are missing' do