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
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_device_bn_hummingbird into cd-4.4