WSEventLoop: Remove inheritance from CEventLoop

The only reason for the inheritance was to add FDs to the select set.

Since CNotifier is available (and now also quite useful), we can make use of it
instead, and remove the inheritance.

Servers/WindowServer/main.cpp

@@ -27,6 +27,6 @@ int main(int, char**)
     WSWindowManager window_manager;
 
     dbgprintf("Entering WindowServer main loop.\n");
-    WSEventLoop::the().exec();
+    loop.exec();
     ASSERT_NOT_REACHED();
 }