mail: revert ~IMAPProtocol

Waiting of worker threads in IMAPProtocol destructor introducred new deadlocks.

For example: fWorkerLock grabbed in destructor leads to deadlock with 
CheckSubscribedFoldersCommand (which grabs this lock with flock grabbed).

So, currently it should be reverted.

Change-Id: Ibc4b4f85300352e045d4ce72deb804e0e613f25c
Reviewed-on: https://review.haiku-os.org/714
Reviewed-by: waddlesplash <[email protected]>

src/add-ons/mail_daemon/inbound_protocols/imap/IMAPProtocol.cpp

@@ -38,15 +38,6 @@ IMAPProtocol::IMAPProtocol(const BMailAccountSettings& settings)
 
 IMAPProtocol::~IMAPProtocol()
 {
-	MutexLocker locker(fWorkerLock);
-	for (int32 i = 0; i < fWorkers.CountItems(); i++)
-		fWorkers.ItemAt(i)->Quit();
-	int tries = 10;
-	while (fWorkers.CountItems() > 0 && --tries > 0) {
-		locker.Unlock();
-		snooze(500000);
-		locker.Lock();
-	}
 }