Remove swipe to exit persistent Vr mode behavior

This behavior is somewhat redundant now
* It is currently already possible to exit Vr mode in normal
circumstances by pressing the X in the top left of the screen.
* If a 'safety hatch' is needed, one can just press the power button,
which will require going through the Don flow again, which can then be
cancelled by pressing the X button.

As it is, the swipe behavior is likely just to cause confusion (and
currently, it puts the device in a bad state where the vr app is still
running, but the screen is blank except for the overlay). My proposition
is just to remove it and use the power button as the safe/guaranteed way
to exit vr mode.

Bug: 36965697
Test: Swiping no longer drops the screen to the overlay when in a
vrflinger application.

Change-Id: I461828f5dce67361a5f4d60c47ac7d6371a4efb3