Make CSS agnostic to underlying profile image size
Summary: Ref T7707. My analysis there was a bit confused and this isn't really all that important, but seems cleaner and desirable to be agnostic to the underlying image size.
Test Plan: Tested Safari, Firefox and Chrome with a variety of profile image sizes.
Reviewers: chad, btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T7707
Differential Revision: https://secure.phabricator.com/D12825