Remove preserve surface block when detaching children.

This code path was added with the idea of avoiding the bug where
children have been detached but then the client receives the same surface
back. However it seems this idea doesn't really work, there's no hint
to the client side to ensure that the SurfaceView is recreated, in
particular SurfaceView.java does not check the generation ID of the Surface
changing. This means this fix wasn't really working, as the children would
just keep trying to use the old detached SurfaceView. The fix is also adding
complexity by introducing extra surfaces when quitting apps.

Bug: 79748420
Test: go/wm-smoke. Manual
Change-Id: I281c748aa4ccc8de04abebbd4f030ceb3f301ba1