Revert Change I5ec0e757: Don't enable the light sensor if it's not being used

Light sensor is only used anyway in changed function if mUseSoftwareAutoBrightness is true.  Setting mAutoBrightnessEnabled to true and checking that flag also will make no difference to the end result.

Change-Id: Iaf78a908f22fb8a52661385def602aabbbbf5643