Revert "Revert using an event object for waking up event loop in wxMSW"

This reverts commit ebb3a791b9,
effectively reapplying 6c40531fb7 once
again.

This breaks wake up when not running our own event loop once again
(see #17579), but this will be fixed in the next commit.

include/wx/msw/evtloop.h

@@ -53,7 +53,6 @@ public:
     // override/implement base class virtuals
     virtual bool Dispatch() wxOVERRIDE;
     virtual int DispatchTimeout(unsigned long timeout) wxOVERRIDE;
-    virtual void WakeUp() wxOVERRIDE;
 
 protected:
     virtual void OnNextIteration() wxOVERRIDE;