SurfaceFlinger_test: disable flaking child test

SurfaceFlinger_test.ChildLayerTest#ChildrenSurviveParentDestruction
has been breaking presubmit runs for more than one month with
no action.

Bug: 243597796
Test: SurfaceFlinger_test, TEST_MAPPING
Change-Id: I1f6b4a0756ef112624a1657246b280149a432fdd
1 file changed