glapi: no longer emit #include "mfeatures.h" in generated files

None of the symbols in mfeatures.h are used anymore.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/mapi/glapi/gen/gl_genexec.py

@@ -44,7 +44,6 @@ header = """/**
  */
 
 
-#include "main/mfeatures.h"
 #include "main/accum.h"
 #include "main/api_loopback.h"
 #include "main/api_exec.h"