New Pipeline: Don't skip detaching children; it causes crashes if they are...

New Pipeline: Don't skip detaching children; it causes crashes if they are attached later to a different parent.

Fixes: 211574810
Test: I had a reliable repro when building http://ag/q/topic:b194287800_test_empty_shade, and this resolved it.
Change-Id: I7974b471630c767b8bbf6d44434dd68bd103cb01