Don't require a transaction to mark a participant up-to-date

Summary:
Pathway to D17685. We no longer have "behindTransactionPHID", so we no longer need the latest transaction.

This allows some code to be removed.

Test Plan:
- Grepped for callsites to `markUpToDate()` and variables used in the calls.
- Sent messages in a couple threads, viewed them, saw unread counts go away.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D17733

src/applications/conpherence/controller/ConpherenceColumnViewController.php

···
       $transactions = $conpherence->getTransactions();
       $latest_transaction = head($transactions);
       $write_guard = AphrontWriteGuard::beginScopedUnguardedWrites();
-      $participant->markUpToDate($conpherence, $latest_transaction);
+      $participant->markUpToDate($conpherence);
       unset($write_guard);
 
       $draft = PhabricatorDraft::newFromUserAndKey(

src/applications/conpherence/controller/ConpherenceUpdateController.php

···
       $key = PhabricatorConpherenceColumnMinimizeSetting::SETTINGKEY;
       $minimized = $user->getUserSetting($key);
       if (!$minimized) {
-        $participant->markUpToDate($conpherence, $data['latest_transaction']);
+        $participant->markUpToDate($conpherence);
       }
     } else if ($need_transactions) {
       $non_update = true;

src/applications/conpherence/controller/ConpherenceViewController.php

···
     }
     $this->setConpherence($conpherence);
 
-    $transactions = $this->getNeededTransactions(
-      $conpherence,
-      $old_message_id);
-    $latest_transaction = head($transactions);
     $participant = $conpherence->getParticipantIfExists($user->getPHID());
     if ($participant) {
       if (!$participant->isUpToDate($conpherence)) {
         $write_guard = AphrontWriteGuard::beginScopedUnguardedWrites();
-        $participant->markUpToDate($conpherence, $latest_transaction);
+        $participant->markUpToDate($conpherence);
         $user->clearCacheData(PhabricatorUserMessageCountCacheType::KEY_COUNT);
         unset($write_guard);
       }
···
           ->setText(pht('Login to Participate'))
           ->setHref((string)$login_href));
     }
-  }
-
-  private function getNeededTransactions(
-    ConpherenceThread $conpherence,
-    $message_id) {
-
-    if ($message_id) {
-      $newer_transactions = $conpherence->getTransactions();
-      $query = id(new ConpherenceTransactionQuery())
-        ->setViewer($this->getRequest()->getUser())
-        ->withObjectPHIDs(array($conpherence->getPHID()))
-        ->setAfterID($message_id)
-        ->needHandles(true)
-        ->setLimit(self::OLDER_FETCH_LIMIT);
-      $older_transactions = $query->execute();
-      $handles = array();
-      foreach ($older_transactions as $transaction) {
-        $handles += $transaction->getHandles();
-      }
-      $conpherence->attachHandles($conpherence->getHandles() + $handles);
-      $transactions = array_merge($newer_transactions, $older_transactions);
-      $conpherence->attachTransactions($transactions);
-    } else {
-      $transactions = $conpherence->getTransactions();
-    }
-
-    return $transactions;
   }
 
   private function getMainQueryLimit() {

src/applications/conpherence/storage/ConpherenceParticipant.php

···
     return nonempty($this->settings, array());
   }
 
-  public function markUpToDate(
-    ConpherenceThread $conpherence,
-    ConpherenceTransaction $xaction) {
+  public function markUpToDate(ConpherenceThread $conpherence) {
 
     if (!$this->isUpToDate($conpherence)) {
       $this->setSeenMessageCount($conpherence->getMessageCount());