Remove incorrect localVue usage in ee/spec/frontend

What does this MR do?

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

Involved specs

• ee/spec/frontend/analytics/productivity_analytics/components/app_spec.js
• ee/spec/frontend/analytics/productivity_analytics/components/filter_dropdowns_spec.js
• ee/spec/frontend/approvals/components/modal_rule_remove_spec.js
• ee/spec/frontend/environments_dashboard/components/dashboard_spec.js
• ee/spec/frontend/feature_flags/components/edit_feature_flag_spec.js
• ee/spec/frontend/subscriptions/new/components/checkout/components/step_spec.js
• ee/spec/frontend/threat_monitoring/components/waf_statistics_summary_spec.js
• spec/frontend/diffs/components/settings_dropdown_spec.js
• spec/frontend/frequent_items/components/frequent_items_search_input_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: #195864 (closed)