chore(magnification): cleanup...

chore(magnification): cleanup do_not_check_intersection_when_non_magnifiable_window_transitions flag usage

In ag/25446076 we add the flag to verify the bug fix with rollout process. Since the flag have completed the trunkfood stage, as "Flag Cleanup Policy" we will first remove the flag usage in codebase, then remove the flag decalration after.

Bug: 312624253
Flag: com.android.window.flags.do_not_check_intersection_when_non_magnifiable_window_transitions
Test: manually
      atest AccessibilityMagnificationTest
Change-Id: I4e6a413ac9717a238ad1ae856e4ab7ebd27ffcc1