Remove a couple of duplicate typedefs.

In GL/gl.h, remove PFNGLBLENDCOLORPROC, PFNGLBLENDEQUATIONPROC, and the
GL_OES_EGL_image section.

PFNGLBLENDCOLORPROC and PFNGLBLENDEQUATIONPROC are defined in GL/glext.h in the
GL_VERSION_1_4 section.

GL_OES_EGL_image is defined in GLES/glext.h and GLES2/gl2ext.h, and the
GLeglImageOES typedef is also defined in GL/glext.h under
GL_EXT_EGL_image_storage.