Fixes issue with nav icon tooltips in safari

What does this MR do?

Removes an overflow style causing issues with safari.

How confident are you it won't break things if deployed?

Tested and working correctly in Firefox and Safari 11, probably needs a bit more testing.

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))