Remove "target branch advanced" warning from FE code (EE)

Removes the "target branch advanced" warning from the frontend
as it is no longer needed due to the new merge trains feature.

ee/app/assets/javascripts/vue_merge_request_widget/mr_widget_options.vue

@@ -322,18 +322,6 @@ export default {
             }}
           </mr-widget-alert-message>
 
-          <mr-widget-alert-message
-            v-if="showTargetBranchAdvancedError"
-            type="danger"
-            :help-path="mr.mergeRequestPipelinesHelpPath"
-          >
-            {{
-              s__(
-                'mrWidget|The target branch has advanced, which invalidates the merge request pipeline. Please update the source branch and retry merging',
-              )
-            }}
-          </mr-widget-alert-message>
-
           <mr-widget-alert-message v-if="mr.mergeError" type="danger">
             {{ mergeError }}
           </mr-widget-alert-message>

ee/spec/features/merge_request/user_sees_merge_widget_spec.rb

@@ -45,21 +45,6 @@ describe 'Merge request > User sees merge widget', :js do
 
         expect(page).not_to have_css('.danger_message')
       end
-
-      context 'when target branch is advanced' do
-        let(:options) { { target_sha: 'old-commit' } }
-
-        it 'shows a warning that fork project cannot create merge request pipelines' do
-          visit project_merge_request_path(project, merge_request)
-
-          within('.danger_message') do
-            expect(page)
-              .to have_content('The target branch has advanced, which invalidates ' \
-                               'the merge request pipeline. Please update the source ' \
-                               'branch and retry merging')
-          end
-        end
-      end
     end
 
     context 'when merge request is submitted from a forked project' do

locale/gitlab.pot

@@ -16332,9 +16332,6 @@ msgstr ""
 msgid "mrWidget|The source branch will not be deleted"
 msgstr ""
 
-msgid "mrWidget|The target branch has advanced, which invalidates the merge request pipeline. Please update the source branch and retry merging"
-msgstr ""
-
 msgid "mrWidget|There are merge conflicts"
 msgstr ""