msm: HTC: minor set_backlight function cleanup

* Remove pass-through set_backlight functions
* Remove stored backlight values: these were either unused or redundant
  to the checks performed in msm_fb.c

Change-Id: I75e3accb635831ed1f6b00e57ecd089778142c8d
valentewx: minor set_backlight function cleanup
cm3629: Restore stock sleeps

The sleeps inside lightsensor_enable are necessary to prevent the
backlight work queue filling before sensor values are ready. The sleep
inside psensor_enable seems to not be necessary, so it remains excluded,
cutting down on screen-on lag.

Change-Id: I107d7c09d199b332bf192a1c6e5f83be44e8dc7f