Revert "Fix fields initialization in wxCommandEvent copy ctor."

This reverts commit 62763ad541 which seems to
have been completely unnecessary as the fields had been already initialized
and this commit actually broke initialization of the propagation level of the
copied wxCommandEvent objects.

Add a unit test proving that things do work.

Closes #16739.

include/wx/event.h

@@ -1502,8 +1502,10 @@ public:
     {
         m_clientData = NULL;
         m_clientObject = NULL;
+        m_isCommandEvent = true;
 
-        Init();
+        // the command events are propagated upwards by default
+        m_propagationLevel = wxEVENT_PROPAGATE_MAX;
     }
 
     wxCommandEvent(const wxCommandEvent& event)
@@ -1516,8 +1518,6 @@ public:
         // need to copy it explicitly.
         if ( m_cmdString.empty() )
             m_cmdString = event.GetString();
-
-        Init();
     }
 
     // Set/Get client data from controls
@@ -1549,13 +1549,6 @@ protected:
     wxClientData*     m_clientObject;  // Arbitrary client object
 
 private:
-    void Init()
-    {
-        m_isCommandEvent = true;
-
-        // the command events are propagated upwards by default
-        m_propagationLevel = wxEVENT_PROPAGATE_MAX;
-    }
 
     wxDECLARE_DYNAMIC_CLASS_NO_ASSIGN(wxCommandEvent);
 };