conf: Remove unnecessary checks in virSecurityLabelDefsParseXML

Failure would have occurred for @ctxt before in callers' other
virXPath calls and @def derefs.

Found by Coverity due to commit 66a508d2 using VIR_XPATH_NODE_AUTORESTORE
to access @ctxt before the if condition. The @def was noted by review.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/conf/domain_conf.c

@@ -8516,10 +8516,6 @@ virSecurityLabelDefsParseXML(virDomainDefPtr def,
     virCapsHostPtr host = &caps->host;
     VIR_AUTOFREE(xmlNodePtr *) list = NULL;
 
-    /* Check args and save context */
-    if (def == NULL || ctxt == NULL)
-        return 0;
-
     /* Allocate a security labels based on XML */
     if ((n = virXPathNodeSet("./seclabel", ctxt, &list)) < 0)
         goto error;