FreeBSD: Prune some unneeded definitions

IS_XATTRDIR is never used.
v_count is only used in two places, one immediately followed by the
use of the real name, v_usecount.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@ixsystems.com>
Closes openzfs#11973

include/os/freebsd/spl/sys/vnode.h

@@ -66,13 +66,8 @@ typedef	struct vop_vector	vnodeops_t;
 #define	vop_fid_args	vop_vptofh_args
 #define	a_fid		a_fhp
 
-#define	IS_XATTRDIR(dvp)	(0)
-
-#define	v_count	v_usecount
-
 #define	rootvfs		(rootvnode == NULL ? NULL : rootvnode->v_mount)
 
-
 #ifndef IN_BASE
 static __inline int
 vn_is_readonly(vnode_t *vp)

module/os/freebsd/spl/spl_vfs.c

@@ -275,7 +275,7 @@ mount_snapshot(kthread_t *td, vnode_t **vpp, const char *fstype, char *fspath,
 void
 vn_rele_async(vnode_t *vp, taskq_t *taskq)
 {
-	VERIFY(vp->v_count > 0);
+	VERIFY(vp->v_usecount > 0);
 	if (refcount_release_if_not_last(&vp->v_usecount)) {
 #if __FreeBSD_version < 1300045
 		vdrop(vp);

module/os/freebsd/zfs/zfs_vfsops.c

@@ -1592,7 +1592,7 @@ zfsvfs_teardown(zfsvfs_t *zfsvfs, boolean_t unmounting)
 	for (zp = list_head(&zfsvfs->z_all_znodes); zp != NULL;
 	    zp = list_next(&zfsvfs->z_all_znodes, zp))
 		if (zp->z_sa_hdl) {
-			ASSERT(ZTOV(zp)->v_count >= 0);
+			ASSERT(ZTOV(zp)->v_usecount >= 0);
 			zfs_znode_dmu_fini(zp);
 		}
 	mutex_exit(&zfsvfs->z_znodes_lock);