Unify code paths for collapsing action views in action bars

This reverts a well-intentioned bugfix that made
ActionBarOverlayLayout focusable in touch mode and caused issues with
some activity layouts. Removes the associated key handling code for
the Back key in ActionBarOverlayLayout and handles it at a higher
level in Activity instead. (This same code path was already in use by
ToolbarActionBar.)

Bug 17105724

Change-Id: I57e4cace44a6d11f25a2549644b565446d616a52