fix double free in acme.

in acmerrorproc():
		sendp(s);
		free(s);

	in waitthread():
		recv(&err)
		free(err)

	We only want waitthread to free.

sys/src/cmd/acme/acme.c

@@ -316,7 +316,6 @@ acmeerrorproc(void *)
 		buf[n] = '\0';
 		s = estrdup(buf);
 		sendp(cerr, s);
-		free(s);
 	}
 	free(buf);
 }