Cleanup split screen offset in TaskViewSimulator

- Removed mRunningTargetWindowPosition and mSplitOffset, as they countered each other out anyway
- Removed PagedOrientationHandler#setLeashSplitOffset() since it's no longer used

Test: Swipe up from split and non split apps in both orientations on large and small devices, with and without home rotation enabled
Bug: 200817624
Change-Id: I78a80cbc718ee38a8933fa323798fb436710d59f