Admin bar: Add CSS to hide icons in "Edit" submenu

[ryelle]

Fixes WordPress/wordcamp.org#1259 — This is just a visual issue on WordCamp sites, where each item is offset like a staircase due to the icons. Submenu items don't need icons, so this just removes them, which is the same behavior as the rest of wporg.

Before	After

This should have no effect on the w.org sites, since they already have CSS that does this (from the global header CSS).

To test

• Sync this file to the WordCamp pub-sync location
• View any WordCamp site you have admin permissions on (to see both Customize and Edit Site)
• Hover over the "Edit …" item in the admin bar
• The dropdown should be in alignment, and not have icons