Revert "block: Let replace_child_noperm free children"

Revert "block: Let replace_child_noperm free children"

We are going to reimplement this behavior (clear bs->file / bs->backing
pointers automatically when child->bs is cleared) in a nicer way, see
further commit
"block: Manipulate bs->file / bs->backing pointers in .attach/.detach".

With this revert we bring back a problem that was fixed by b0a9f6fed3d8.
Still the problem was mostly theoretical, we don't have concrete bugs
fixed by b0a9f6fed3d8, we don't have a specific test. Probably some
accidental failures of iotests are related.

Alternatively, we may merge this and following three reverts into final
"block: Manipulate ..." to avoid any kind of regression. But seems that
in this case having separate clear revert commits is better.

This reverts commit b0a9f6fed3d80de610dcd04a7e66f9f30a04174f.

Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
Reviewed-by: Hanna Reitz <[email protected]>
Message-Id: <20220726201134[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>