Remove QsLog destinations when they are destroyed.

This fixes some issues where MultiMC was segfaulting on exit because
things were trying to write to the logger while they were being destroyed,
but the destinations had already been destroyed and were left in the list.

logger/QsLog.cpp

@@ -134,4 +134,9 @@ void Logger::write(const QString &message)
 	}
 }
 
+void Logger::removeDestination(Destination* destination)
+{
+	d->destList.removeAll(destination);
+}
+
 } // end namespace