zpl_xattr.c: Remove HAVE_XATTR_HANDLER_NAME

`HAVE_XATTR_HANDLER_NAME` was removed in upstream commit 79c307d. Remove
it from our truenas branch as well.

Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>

module/os/linux/zfs/zpl_xattr.c

@@ -1750,10 +1750,8 @@ __zpl_xattr_nfs41acl_get(struct inode *ip, const char *name,
 	size_t xdr_size;
 
 	/* xattr_resolve_name will do this for us if this is defined */
-#ifndef HAVE_XATTR_HANDLER_NAME
 	if (strcmp(name, "") != 0)
 		return (-EINVAL);
-#endif
 
 	if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_NFSV4)
 		return (-EOPNOTSUPP);