HPCC-19690 Embed activity without output not executing

- TAKexternalsink was running as CExternalSlaveActivity
- TAKexternalsink is now running as CExternalSlaveSinkActivity

Signed-off-by: James McMullan <james.mcmullan@lexisnexis.com>

thorlcr/slave/slave.cpp

@@ -766,10 +766,12 @@ public:
                 ret = createStreamedIteratorSlave(this);
                 break;
             case TAKexternalprocess:
-            case TAKexternalsink:
             case TAKexternalsource:
                 ret = createExternalSlave(this);
                 break;
+            case TAKexternalsink:
+                ret = createExternalSinkSlave(this);
+                break;
             default:
                 throw MakeStringException(TE_UnsupportedActivityKind, "Unsupported activity kind: %s", activityKindStr(kind));
         }