Promote PIP postsubmit tests to presubmit

The tests have been stable for the past 2 weeks in postsubmit and can be promoted to presubmit

Test: atest FlickerTests:com.android.wm.shell.flicker.pip
Bug: 174238224
Change-Id: Ie7cbd56940e4b5eacd25ba38d1fd0a5966b9a7e9