Fix coverity UNUSED_VALUE findings in core support level files

Most of these were just saving returned values without using them and
in some cases the variable being saved to could be removed as well.

(issue ASTERISK-19672)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@368738 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -13549,7 +13549,7 @@ static int transmit_refer(struct sip_pvt *p, const char *dest)
 		ast_log(LOG_NOTICE, "From address missing 'sip(s):', assuming sip:\n");
 	}
 	/* Get just the username part */
-	if ((c = strchr(dest, '@'))) {
+	if (strchr(dest, '@')) {
 		c = NULL;
 	} else if ((c = strchr(of, '@'))) {
 		*c++ = '\0';