[waitForAllWindowsDrawn] Wait for transitions only on default displays

Waiting for Shell transition is implemented only
for default display, but we call mDisplayUpdater.waitForTransition()
even for non-default display which might cause
the screen unblock message to be overwritten.

Test: atest DisplayContentDeferredUpdateTests
Bug: 353204414
Flag: EXEMPT bugfix
Change-Id: I791ecde84c7a1a2b2d987a73900d03926c32b4f3