Fix Battery optimization page broken

- mCompositeFilter is not changed after toggling filter, so the
list items are not changing. Fixed by changing mCompositeFilter
after toggle is changed.
- Because mSession.rebuild returns null, removes some dead code.

Fixes: 149362024
Test: 1. Settings > App & notifications > Special app access >
         Battery optimization
      2. Toggle Not optimized and All apps
      3. App list should change after step 2

Change-Id: Ifd5c7b0f1d809ae7a49d62b39e34fa899700326c