Fix Tapl Background.switchToOverview for tablets

- The test failed because of unexpected touch event recoreded
- This is because it does not expect the gesture to start from launcher. But with taskbar present, the touch will be recorded from taskbar

Bug: 191344757
Test: TaplTestsQuickStep
Change-Id: I09b5a3029eef5cdc874bbbe8653976f12136144c