Fix automatic lifecycle delete stacking

Fix automatic lifecycle delete stacking

Nodes with automatic lifecycle have the strange property that their
delete operations may actually stack with other operations.

Unfortunately delete operation itself has no semantics of having
underlying modifications, as it has no baseline to which to apply
them.

In order to fix this, we need to turn deletes into empty writes
for these constructs and once we are performing disappearing, undo
this trick. This effectively means that both empty writes and deletes
result in a delete operation, if they ended up modifying the tree,
or into a no-op if they did not.

JIRA: YANGTOOLS-938
Change-Id: I68b9f304e76d6b1bdb707f411a87cd6085ed8bc7
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>