Rename custom recovery keymapping file to match original source

The corresponding keymapping file in the recovery source is now
default_recovery_keys.c, and recovery_ui now typically refers to a
separate device-overridable file (which we want to override in the
future).

Change-Id: I0bde1213fcae08a61915b98da726972122dd65d2
recovery_ui: update for CWM API changes

CWM's eliminating device_toggle_display() and
ui_get_showing_back_button() (see http://review.cyanogenmod.org/62724).
Remove these in our recovery_ui.c.

Change-Id: Ib26ffdf04194dc0f916934bf1bc1b92b47938ee2