Clean up dead code from SwipeHelper

Clean up the dead codes from SwipeHelper to make logics cleaner and
make bug-fixings straightforward.

Cleaned codes:

mDisableHwLayers: always false
setDisableHardwareLayers: never called
CONSTRAIN_SWIPE, FADE_OUT_DURING_SWIPE, DISMISS_IF_SWIPED_FAR_ENOUGH:
always true
X, Y: never used

Fix: 358695203
Bug: 355132257
Test: atest SystemUITests
Flag: EXEMPT refactor
Change-Id: I2ccb344a90fa090b96e7f9c938da969212a34a5b