[core] rm GLconstants header unused since 19 years

README/ReleaseNotes/v642/index.md

@@ -67,6 +67,7 @@ Users are encouraged to export their models to ONNX and use the retained ONNX pa
 * The `RooTrace` class is deprecated and will be removed in ROOT 6.44. It was a RooFit-specific memory tracer whose instrumentation hooks are compiled out by default, so it has been inert and untested for years. For memory debugging, please use general-purpose tools such as AddressSanitizer or Valgrind instead.
 * Support for the AIX operating system has been removed from the codebase. This support has not been tested since the late v5 releases and the LLVM JIT is not yet supporting AIX.
 * The headers Htypes.h and Gtypes.h that were deprecated in ROOT 6.20 will now emit warnings and will be fully removed in ROOT 6.44.
+* The header GLConstants.h is no longer part of ROOT installed headers.
 
 ## Build System
 

core/base/inc/TVirtualGL.h

@@ -30,7 +30,6 @@
 
 #include "TNamed.h"
 #include "GuiTypes.h"
-#include "GLConstants.h"
 
 class TVirtualViewer3D;
 class TPoints3DABC;