Remove ENABLE_OVERVIEW_ACTIONS flag, defaulting to true

We no longer support the "peeking" model where the shelf would
peek on motion pause from an app and overview would peek on motion
pause from home. Thus, removed/inlined the following:
- FlingAndHoldTouchController (merged into its sole subclass
  NoButtonNavbarToOverviewTouchController)
- ShelfPeekAnim
- OverviewPeekState

Change-Id: I066a3ad2636fde4786089c922b896bf1e03361fd
27 files changed