switch the remnants of releasing the mountpoint away from fs_pin

We used to need rather convoluted ordering trickery to guarantee
that dput() of ex-mountpoints happens before the final mntput()
of the same.  Since we don't need that anymore, there's no point
playing with fs_pin for that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/fs_pin.h

@@ -20,6 +20,5 @@ static inline void init_fs_pin(struct fs_pin *p, void (*kill)(struct fs_pin *))
 }
 
 void pin_remove(struct fs_pin *);
-void pin_insert_group(struct fs_pin *, struct vfsmount *, struct hlist_head *);
 void pin_insert(struct fs_pin *, struct vfsmount *);
 void pin_kill(struct fs_pin *);