Archive sessions whenever an identity key changes

Sessions established with the previous identity should no longer be used for
sending, so we should close them.

Since we've added this call to saveIdentity, we can omit the call to it after
profile fetches.

// FREEBIE

js/models/conversations.js

@@ -569,11 +569,7 @@
 
             return textsecure.storage.protocol.saveIdentity(
                 id, identityKey, false
-            ).then(function(isIdentityChange) {
-                if (isIdentityChange) {
-                    return textsecure.storage.protocol.archiveAllSessions(id);
-                }
-            });
+            );
         });
     },