rc: squelch 'Write error' warning

When writing to a large variable in /env, we
spam 'Write error', in spite of the env var
working. This is new behavior, as of commit
b90036a062.

It produces a lot of scary, noisy warnings,
which are probably bogus.

sys/src/cmd/rc/io.c

@@ -275,7 +275,6 @@ flushio(io *f)
 	else{
 		n = f->bufp - f->buf;
 		if(n && Write(f->fd, f->buf, n) != n){
-			Write(2, "Write error\n", 12);
 			if(ntrap)
 				dotrap();
 		}