docs: address review feedback on migrated plugin docs

- Update internationalization page to use new frontend system patterns
  (TranslationBlueprint from @backstage/plugin-app-react instead of
  createApp __experimentalTranslations)
- Fix AnalyticsImplementationBlueprint import to use @backstage/plugin-app-react
- Remove search integration page from frontend-system section as it
  belongs in the core feature search docs

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

microsite/sidebars.ts

@@ -546,7 +546,6 @@ export default {
                 'frontend-system/building-plugins/internationalization',
                 'frontend-system/building-plugins/analytics',
                 'frontend-system/building-plugins/feature-flags',
-                'frontend-system/building-plugins/integrating-search-into-plugins',
               ],
             ),
             sidebarElementWithIndex(