Added code to force reloading of panda_glext.h

panda/src/glstuff/panda_glext.h

@@ -1,8 +1,3 @@
-/* Additions by drose to re-include this glext.h even if an older
-   version has previously been included. */
-#if defined(GL_GLEXT_VERSION) && GL_GLEXT_VERSION < 29
-  #undef GL_GLEXT_VERSION
-#endif
 #ifndef GL_GLEXT_VERSION
 
 #ifdef __cplusplus