vfs: convert recycles_count and recycles_free_count to mere u_long

Only vnlru ever updates them.

This also removes recycles_count updates from hand-rolled debug vnode
recycling via sysctl.

Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 37544d9768110fd67527db7f2a3f7bb6fc977582)