Don't show "master (branched from master)" in UI

Summary:
Ref T3462. If someone works directly on `master`, we currently show "Branch: master (branched from master)" in the UI.

Although this is sort of technically accurate, it is confusing.

Instead, just show "Branch: master" in this situation.

Test Plan: Saw "master" instead of "master (branched from master)".

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T3462

Differential Revision: https://secure.phabricator.com/D14829

src/applications/differential/customfield/DifferentialBranchField.php

@@ -45,7 +45,7 @@ final class DifferentialBranchField
       return pht('%s (bookmark)', $bookmark);
     } else if (strlen($branch)) {
       $onto = $diff->loadTargetBranch();
-      if (strlen($onto)) {
+      if (strlen($onto) && ($onto !== $branch)) {
         return pht(
           '%s (branched from %s)',
           $branch,