Remove the GLES2 wrapper

The GLES2 wrapper is no longer needed because the shader generation is
done within the GLSL fragend and vertend and any functions that are
different for GLES2 are now guarded by #ifdefs.

cogl/cogl-context.c

@@ -245,11 +245,15 @@ cogl_create_context (void)
 
   _context->texture_download_pipeline = COGL_INVALID_HANDLE;
 
+#ifndef HAVE_COGL_GLES2
   /* The default for GL_ALPHA_TEST is to always pass which is equivalent to
    * the test being disabled therefore we assume that for all drivers there
    * will be no performance impact if we always leave the test enabled which
-   * makes things a bit simpler for us. */
+   * makes things a bit simpler for us. Under GLES2 the alpha test is
+   * implemented in the fragment shader so there is no enable for it
+   */
   GE (glEnable (GL_ALPHA_TEST));
+#endif
 
 #ifdef HAVE_COGL_GLES2
   _context->flushed_modelview_stack = NULL;