Stop "join project" from trying to write an inverse edge on Users

Summary: Now that Users implement PhabricatorApplicationTransactionInterface, we try to write an inverse edge. At least for now, we should retain the old behavior instead.

Test Plan:
  - Unit tests which cover this stuff pass again.
  - Grepped for other `instanceof PhabricatorApplicationTransactionInterface`, the all seemed either benign or irrelevant.

Reviewers: joshuaspence, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D13215

src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php

@@ -2904,6 +2904,13 @@ abstract class PhabricatorApplicationTransactionEditor
         continue;
       }
 
+      if ($node instanceof PhabricatorUser) {
+        // TODO: At least for now, don't record inverse edge transactions
+        // for users (for example, "alincoln joined project X"): Feed fills
+        // this role instead.
+        continue;
+      }
+
       $editor = $node->getApplicationTransactionEditor();
       $template = $node->getApplicationTransactionTemplate();
       $target = $node->getApplicationTransactionObject();