maple_tree: Use mas_topiary_subtree() in mas_topiary_replace()

maple_tree: Use mas_topiary_subtree() in mas_topiary_replace()

Instead of building a linked list of subtrees to later destroy, do the
destroy once a subtree is identified as replaced.  This will evict the
readers sooner from the dead subtree, but since the common ancestor is
already marked as dead, the transition to the new data will still occur
giving the readers a consistent view of either old or new data.  The
readers will not be able to transition back from new to old data.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>