recovery_keys: 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.

Signed-off-by: Alberto97 <albertop2197@gmail.com>
Merge pull request #17 from Alberto97/cm-11.0

recovery_keys: update for CWM API changes