Remove redundant wxGenericProgressDialog::m_parentTop assignment

The line setting m_parentTop directly was mistakenly left over even
after 7e08367534 added the call to
SetTopParent() just above it.

Remove it now (better late than never), it's redundant at best and even
wrong if the top level parent can't be used as the dialog parent because
SetTopParent() checks for this but this line did not.

src/generic/progdlgg.cpp

@@ -144,7 +144,6 @@ bool wxGenericProgressDialog::Create( const wxString& title,
 {
     SetTopParent(parent);
 
-    m_parentTop = wxGetTopLevelParent(parent);
     m_pdStyle = style;
 
     wxWindow* const