Revert b58ca5df0bb7 ("vfs: remove the now unused insmntque1")

I was somehow convinced that insmntque calls insmntque1 with a NULL
destructor. Unfortunately this worked well enough to not immediately
blow up in simple testing.

Keep not using the destructor in previously patched filesystems though
as it avoids unnecessary casts.

Noted by: kib
Reported by: pho