Mail server: fix disabling notifications

* The default notifier didn't always take the setting into account.
* The mail server was not using the setting from the settings file and
instead waiting for a message that wasn't sent anywhere.

Fixes #10852.

headers/private/mail/MailPrivate.h

@@ -22,7 +22,6 @@ const uint32 kMsgCheckMessage = 'mnow';
 const uint32 kMsgSendMessages = 'msnd';
 const uint32 kMsgSettingsUpdated = 'mrrs';
 const uint32 kMsgAccountsChanged = 'macc';
-const uint32 kMsgSetStatusWindowMode = 'shst';
 const uint32 kMsgCountNewMessages = 'mnum';
 const uint32 kMsgMarkMessageAsRead = 'mmar';
 const uint32 kMsgFetchBody = 'mfeb';