largefiles: remove the `changing_parents` context in `openlfdirstate`

This code might run in any kind of change context, we should rely on the higher
level context instead of opening our own.

hgext/largefiles/lfutil.py

@@ -233,7 +233,6 b' def openlfdirstate(ui, repo, create=True'
                 if len(standins) > 0:
                     vfs.makedirs(lfstoredir)
 
-                with lfdirstate.changing_parents(repo):
                     for standin in standins:
                         lfile = splitstandin(standin)
                         lfdirstate.hacky_extension_update_file(