Fix intermittent PIP crash.

Looks like this is caused by calling removeView right before addView, which happens when we recreate the dismiss target. Sometimes, removeView has not completed by the time we addView again.

I wasn't able to reproduce the crash, but other places in sysui use removeViewImmediate for this purpose.

Bug: 153551432
Test: try rotating the screen a bunch with a PIP visible
Change-Id: Ic96173c1273b8476280a7daf63340bbe9613b21e