PhoneWindowManager: Don't handle navigation bar visibility when switching to PIE

Right now when restoring full height after disabling immersive if pie mode is
on, navbar isn't showed until panel collapsing cause it should have been showed
(the view even with height zero) called by top swipe gesture that calls requestTransientBars().
Don't touch the API, cleanup old code traces and changes cause in any case navbar has height = 0
and its bottom/right gesture is disabled.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: Id05175a553aad2a5a2b36c3fe4e32a2d071dcc88