Decouple superuser from SessionMetadata

Superuser should only be settable via the tool (see []
which is merged in here but not diffbased, and which removes
the implicit superuser for CharlestonRoad). It is a property
of the request, not of the session (there are no sessions in the tool).
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125204707

java/google/registry/flows/domain/DomainTransferRequestFlow.java

@@ -152,7 +152,7 @@ public class DomainTransferRequestFlow
   @Override
   protected final void verifyTransferRequestIsAllowed() throws EppException {
     verifyUnitIsYears(command.getPeriod());
-    if (!superuser) {
+    if (!isSuperuser) {
       verifyPremiumNameIsNotBlocked(targetId, now, getClientId());
     }
     validateFeeChallenge(