Tuned the back gesture further

Previously the back gesture was slightly
too bouncy, so we toned it down a bit.
We're also tuning the vibration to require
a longer duration for it to lift.
Overall the back animation wasn't working
great because of smearing, so we also
simplified that aspect.

Fixes: 130682266
Test: atest SystemUITests
Change-Id: Iff714ccc28fcba25c9b21155c687e2852c8599b7