lockd: Remove unused typedef

Clean up: Looks like the last usage of this typedef was removed by
commit 026fec7e7c47 ("sunrpc: properly type pc_decode callbacks") in
2017.

Reviewed-by: Jeff Layton <[e-mail]>
Reviewed-by: NeilBrown <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

include/linux/lockd/xdr.h

···
 	u32			fsm_mode;
 };
 
-typedef struct nlm_args nlm_args;
-
 /*
  * Generic lockd result
  */