Disallow two finger edge swipe back

Back gesture is a 3-finger gesture. Currently because a two-finger swipe is recognized as if it's a motion event from on the screen, it triggers edge swipe when the cursor is in the zone. We don't want to allow this behavior

Bug: 283112069
Test: manual
Change-Id: I6b6955fe1f290a7c117986f7b72e31ecc23d04e9