Get rid of unused wxTransformMatrix

As it is stated in matrix.cpp wxTransformMatrix was intended to be used
in wxDC to replace the basic system of scaling/translation but actually
it was never used.
Because applying affine transformations can be done with wxAffineMatrix2D
and wxDC::SetTransformMatrix() we can get rid of this dead code.

Closes #13114.

tests/allheaders.h

@@ -217,7 +217,6 @@
 #include <wx/longlong.h>
 #include <wx/lzmastream.h>
 #include <wx/math.h>
-#include <wx/matrix.h>
 #include <wx/mdi.h>
 #include <wx/mediactrl.h>
 #include <wx/memconf.h>