CLEANUP: check; Remove some useless assignments to NULL

In process_chk_conn(), some assignments to NULL are useless and are reported
by Coverity as unused value. while it is harmless, these assignments can be
removed.

This patch should fix the coverity report #2158.
diff --git a/src/check.c b/src/check.c
index 86cd596..a440185 100644
--- a/src/check.c
+++ b/src/check.c
@@ -1242,7 +1242,6 @@
 			if (check->state & CHK_ST_CLOSE_CONN) {
 				TRACE_DEVEL("closing current connection", CHK_EV_TASK_WAKE|CHK_EV_HCHK_RUN, check);
 				check->state &= ~CHK_ST_CLOSE_CONN;
-				conn = NULL;
 				if (!sc_reset_endp(check->sc)) {
 					/* error will be handled by tcpcheck_main().
 					 * On success, remove all flags except SE_FL_DETACHED
@@ -1277,8 +1276,7 @@
 
 	if (sc) {
 		sc_destroy(sc);
-		sc = check->sc = NULL;
-		conn = NULL;
+		check->sc = NULL;
 	}
 
 	if (check->sess != NULL) {