Remove riscv workaround in sys.netgraph.hub.loop test

The test case now passes on this architecture. This reverts commits
d5fd5cdc06 and 168b579a48.

Reviewed by:	lwhsu, imp
Differential Revision:	https://reviews.freebsd.org/D33252

tests/sys/netgraph/hub.c

@@ -127,11 +127,6 @@ ATF_TC_BODY(loop, dummy)
 	int		i;
 	char		msg[] = "LOOP Alert!";
 
-#if defined(__riscv)
-	if (atf_tc_get_config_var_as_bool_wd(dummy, "ci", false))
-		atf_tc_skip("https://bugs.freebsd.org/259157");
-#endif
-
 	ng_errors(PASS);
 	ng_shutdown("hub1:");
 	ng_shutdown("hub2:");