Revert "Merge pull request #4803 from lucascaton/master"

This reverts commit bb842e8d2111e50b21a14b8bd6d89371a4b9cd68, reversing
changes made to 40c287c7983c20c498f6a8a2ea49e9a6455347f7.
This was causing issues in one of our apps we just upgraded.
ActionController::RoutingError: No route matches [GET]
"/images/favicon.ico"
favicon_link_tag now returns '/images/favicon.ico' and in 3.2 returned
'/favicon.ico'
Browsers by default look for favicon.ico in the root directory

Conflicts:
	actionpack/CHANGELOG.md
	actionpack/lib/action_view/helpers/asset_tag_helper.rb