Revert " Trigger iid logic from GitHub importer for merge requests."

This reverts commit fb98496f.

lib/gitlab/import/merge_request_helpers.rb

@@ -24,10 +24,6 @@ module Gitlab
 
           merge_request = project.merge_requests.reload.find(merge_request_id)
 
-          # We use .insert_and_return_id which effectively disables all callbacks.
-          # Trigger iid logic here to make sure we track internal id values consistently.
-          merge_request.ensure_target_project_iid!
-
           [merge_request, false]
         end
       rescue ActiveRecord::InvalidForeignKey

spec/lib/gitlab/github_import/importer/pull_request_importer_spec.rb

@@ -111,16 +111,6 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
         expect(mr).to be_instance_of(MergeRequest)
         expect(exists).to eq(false)
       end
-
-      it 'triggers internal_id functionality to track greatest iids' do
-        mr = build_stubbed(:merge_request, source_project: project, target_project: project)
-        allow(importer).to receive(:insert_and_return_id).and_return(mr.id)
-        allow(project.merge_requests).to receive(:find).with(mr.id).and_return(mr)
-
-        expect(mr).to receive(:ensure_target_project_iid!)
-
-        importer.create_merge_request
-      end
     end
 
     context 'when the author could not be found' do