Removed call to glEnable for an OpenGL extension to remove errors.

Fixes an ambiguous error message while attempting to enable certain components of OpenGL. Allows me to run demos without a constant stream of 0x500 invalid enum errors. 

In particular, I think that the Intel HD4000 doesn't have support for the GL_DEPTH_BOUNDS_TEST_EXT. Tested briefly on an ATI machine that works fine.