Remove the DEBUG_VFS_LOCKS kernel option

After commit 3bd8fab241 ("vfs: Move DEBUG_VFS_LOCKS checks to
INVARIANTS"), this option has no effect.  Let's finish the removal.

There are a couple of additional uses in zfs, I will submit a separate
patch upstream for them.

Reviewed by:	mckusick, kib
Differential Revision:	https://reviews.freebsd.org/D54662

sys/conf/NOTES

@@ -2673,7 +2673,6 @@ options 	INIT_PATH=/sbin/init:/rescue/init
 
 # Debug options
 options 	BUS_DEBUG	# enable newbus debugging
-options 	DEBUG_VFS_LOCKS	# enable VFS lock debugging
 options 	SOCKBUF_DEBUG	# enable sockbuf last record/mb tail checking
 options 	IFMEDIA_DEBUG	# enable debugging in net/if_media.c
 

sys/conf/options

@@ -601,7 +601,6 @@ BLKDEV_IOSIZE		opt_global.h
 BURN_BRIDGES		opt_global.h
 DEBUG			opt_global.h
 DEBUG_LOCKS		opt_global.h
-DEBUG_VFS_LOCKS		opt_global.h
 DFLTPHYS		opt_global.h
 DIAGNOSTIC		opt_global.h
 INVARIANT_SUPPORT	opt_global.h

sys/conf/std.nodebug

@@ -7,7 +7,6 @@ nooptions	INVARIANT_SUPPORT
 nooptions	DIAGNOSTIC
 nooptions	WITNESS
 nooptions	WITNESS_SKIPSPIN
-nooptions	DEBUG_VFS_LOCKS
 nooptions	BUF_TRACKING
 nooptions	FULL_BUF_TRACKING
 nooptions	DEADLKRES

sys/fs/unionfs/union_subr.c

@@ -1071,7 +1071,7 @@ unionfs_forward_vop_ref(struct vnode *basevp, int *lkflags)
  *    forwarded VOP reacquires the base vnode lock the unionfs vnode
  *    lock will no longer be held.  This can lead to violation of the
  *    caller's sychronization requirements as well as various failed
- *    locking assertions when DEBUG_VFS_LOCKS is enabled.
+ *    locking assertions when INVARIANTS is enabled.
  * 2) Loss of reference on the base vnode.  The caller is expected to
  *    hold a v_usecount reference on the unionfs vnode, while the
  *    unionfs vnode holds a reference on the base-layer vnode(s).  But