conf: Allow disks with identical WWN or serial

Disallowing them broke a use case of testing multipath configurations
for storage. Originally this was added as it was impossible to
use certain /dev/disk-by... links but the disks worked properly.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1349895
(cherry picked from commit 5da28cc3)

src/conf/domain_conf.c

@@ -24339,19 +24339,8 @@ virDomainDiskDefCheckDuplicateInfo(virDomainDiskDefPtr a,
         return -1;
     }
 
-    if (a->wwn && b->wwn && STREQ(a->wwn, b->wwn)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                       _("Disks '%s' and '%s' have identical WWN"),
-                       a->dst, b->dst);
-        return -1;
-    }
-
-    if (a->serial && b->serial && STREQ(a->serial, b->serial)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                       _("Disks '%s' and '%s' have identical serial"),
-                       a->dst, b->dst);
-        return -1;
-    }
+    /* Duplicate WWN/serial isn't usually problematic for the OS and
+     * forbiding it would possibly inhibit using multipath configurations */
 
     return 0;
 }