Break SessionSource out of SessionMetadata and rename it EppRequestSource.

The "SessionSource" has nothing to do with sessions (and it's often
used in sessionless contexts). What it does indicate is the endpoint
used to make the request.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125295224

javatests/google/registry/flows/FlowTestCase.java

@@ -34,7 +34,6 @@ import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Maps;
 
-import google.registry.flows.SessionMetadata.SessionSource;
 import google.registry.flows.picker.FlowPicker;
 import google.registry.model.billing.BillingEvent;
 import google.registry.model.domain.GracePeriod;
@@ -92,13 +91,13 @@ public abstract class FlowTestCase<F extends Flow> {
   protected SessionMetadata sessionMetadata;
   protected FakeClock clock = new FakeClock(DateTime.now(UTC));
   protected TransportCredentials credentials = new PasswordOnlyTransportCredentials();
+  protected EppRequestSource eppRequestSource = EppRequestSource.UNIT_TEST;
 
   @Before
   public void init() throws Exception {
     sessionMetadata = new TestSessionMetadata();
     sessionMetadata.setClientId("TheRegistrar");
     sessionMetadata.setServiceExtensionUris(ProtocolDefinition.getVisibleServiceExtensionUris());
-    sessionMetadata.setSessionSource(SessionSource.NONE);
     ofy().saveWithoutBackup().entity(new ClaimsListSingleton()).now();
     inject.setStaticField(Ofy.class, "clock", clock);  // For transactional flows.
   }
@@ -133,6 +132,7 @@ public abstract class FlowTestCase<F extends Flow> {
         getTrid(),
         sessionMetadata,
         credentials,
+        eppRequestSource,
         commitMode.equals(CommitMode.DRY_RUN),
         userPrivileges.equals(UserPrivileges.SUPERUSER),
         "<xml></xml>".getBytes(),