Clean up obsolete TODO for _setGitSsh()

Change Idcc9808948b018a271b32492766a96876979d1fa addressed the need
for connection context in zuul.merger.merger.Merger.updateRepo() but
failed to remove the TODO comment associated with it. Clean up the
unnecessary comment now.

Change-Id: I57a48a27a09b39efdc4d15f1a3a674b83a1d1199
diff --git a/zuul/merger/merger.py b/zuul/merger/merger.py
index ed98696..0327ab4 100644
--- a/zuul/merger/merger.py
+++ b/zuul/merger/merger.py
@@ -341,10 +341,6 @@
         return self._addProject(hostname, project_name, url, sshkey)
 
     def updateRepo(self, connection_name, project_name):
-        # TODOv3(jhesketh): Reimplement
-        # da90a50b794f18f74de0e2c7ec3210abf79dda24 after merge..
-        # Likely we'll handle connection context per projects differently.
-        # self._setGitSsh()
         repo = self.getRepo(connection_name, project_name)
         try:
             self.log.info("Updating local repository %s/%s",