base: simplify OmniSwitch recents

The handshake between SystemUI and OmniSwitch is nice
but causes issues if one of the parts gets restarted
thanks to android. So simplify it and only use the
settings value. Worst thing that can happen is that
OmniSwitch recents is enabled but OmniSwitch is not running
then nothing will happen if recents is triggered

Change-Id: I43d93ea475f72e55fbc767c65b5050acaf4977eb
Merge pull request #10 from omnirom/android-4.4

base: simplify OmniSwitch recents