Revert "fuse: don't try to write RELEASE/RELEASEDIR reply"

This reverts commit 9dcbb223.

Even though RELEASE is similar to FORGET, it must report back, or
tests will hang.

fuse/server.go

@@ -483,7 +483,7 @@ func (ms *Server) allocOut(req *request, size uint32) []byte {
 func (ms *Server) write(req *request) Status {
 	// Forget/NotifyReply do not wait for reply from filesystem server.
 	switch req.inHeader.Opcode {
-	case _OP_FORGET, _OP_BATCH_FORGET, _OP_NOTIFY_REPLY, _OP_RELEASE, _OP_RELEASEDIR:
+	case _OP_FORGET, _OP_BATCH_FORGET, _OP_NOTIFY_REPLY:
 		return OK
 	case _OP_INTERRUPT:
 		if req.status.Ok() {