Fix profile menu missing on explore page

Fix profile menu missing on explore page

Similar to what we did on https://gitlab.com/gitlab-org/gitter/webapp/merge_requests/1421

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Testing strategy

1. Add the feature toggle, node ./scripts/utils/feature-toggle.js --name vue-left-menu --description "Left menu using Vue (alpha)"
2. Enable the feature toggle
   • Enable: http://localhost:5000/api_web/features/vue-left-menu/1
   • Disable: http://localhost:5000/api_web/features/vue-left-menu/0

Try the following with and without the feature toggle:

1. Visit http://localhost:5000/home/explore
2. Make sure the page is scrollable (probably have to make the viewport smaller)

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1. Sign out
2. Visit http://localhost:5000/explore
3. Make sure the page is scrollable (probably have to make the viewport smaller)

Closes #2166 (closed)