Accessibility: Don't remove checkbox outline on focus

Native checkboxes and radiobuttons on Mac OS X are not fully
styleable. Don't remove the focus ring for those elements because it
makes them less accessible.

Also the outline was removed outside of the focus selector, which
isn't really needed.

Change-Id: I716c84b34b5adb26691f0d4ecd13739de7b8bdbf
Merge "Accessibility: Don't remove checkbox outline on focus"