switch unlock_mount() to namespace_unlock(), convert all umount_tree() callers

which allows to kill the last argument of umount_tree() and make release_mounts()
static.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/pnode.h b/fs/pnode.h
index f4357d3..9eb00ee 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -40,8 +40,7 @@
 unsigned int mnt_get_count(struct mount *mnt);
 void mnt_set_mountpoint(struct mount *, struct mountpoint *,
 			struct mount *);
-void release_mounts(struct list_head *);
-void umount_tree(struct mount *, int, struct list_head *);
+void umount_tree(struct mount *, int);
 struct mount *copy_tree(struct mount *, struct dentry *, int);
 bool is_path_reachable(struct mount *, struct dentry *,
 			 const struct path *root);