build: remove unused @edx/reactifex package

Remove @edx/reactifex package from devDependencies as it is no longer
needed. Translation extraction functionality has been verified to work
correctly without this dependency.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -68,7 +68,6 @@
   },
   "devDependencies": {
     "@edx/browserslist-config": "^1.1.1",
-    "@edx/reactifex": "1.1.0",
     "@openedx/frontend-build": "^14.6.2",
     "babel-plugin-formatjs": "10.5.39",
     "eslint-plugin-import": "2.32.0",