quot: Drop the COMPAT version

We've had this code for 30 years, but there has never been a way to
build it. We have no idea if it still works, or if it ever worked.

Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D53131

(cherry picked from commit 0eaca4a24b97c02685532f86c121a4cf415942c5)