Move UXTheme symbol definitions for Vista+ to msw/uxtheme.h

Remove various definitions and symbol declarations from
numerous files using msw/uxtheme.h to a single file.
When possible vssym32.h is included from the Windows SDK.
For older SDKs tmschema.h is included and missing symbols
are defined in msw/uxtheme.h.

src/msw/window.cpp

@@ -113,14 +113,6 @@
 
 #if wxUSE_UXTHEME
     #include "wx/msw/uxtheme.h"
-    #define EP_EDITTEXT         1
-    #define ETS_NORMAL          1
-    #define ETS_HOT             2
-    #define ETS_SELECTED        3
-    #define ETS_DISABLED        4
-    #define ETS_FOCUSED         5
-    #define ETS_READONLY        6
-    #define ETS_ASSIST          7
 #endif
 
 #if wxUSE_DYNLIB_CLASS