Remove incorrect localVue usage in spec/frontend/vue_mr_widget

What does this MR do?

As described in &2360 (closed), cleans up our Jest tests from unnecessary localVue usage

Involved specs

• spec/frontend/vue_mr_widget/components/artifacts_list_app_spec.js
• spec/frontend/vue_mr_widget/components/artifacts_list_spec.js
• spec/frontend/vue_mr_widget/components/mr_widget_container_spec.js
• spec/frontend/vue_mr_widget/components/mr_widget_icon_spec.js
• spec/frontend/vue_mr_widget/components/states/commit_edit_spec.js
• spec/frontend/vue_mr_widget/components/states/mr_widget_commit_message_dropdown_spec.js
• spec/frontend/vue_mr_widget/components/states/mr_widget_commits_header_spec.js
• spec/frontend/vue_mr_widget/deployment/deployment_view_button_spec.js

Conformity

• Merge request performance guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Closes: #121745 (closed)