This remove cogl-internal.h in favour of using cogl-private.h. Some
things in cogl-internal.h were moved to driver/gl/cogl-util-gl-private.h
and the _cogl_gl_error_to_string function whose prototype was moved from
cogl-internal.h to cogl-util-gl-private.h has had its implementation
moved from cogl.c to cogl-util-gl.c
Reviewed-by: Neil Roberts <neil@linux.intel.com>
(cherry picked from commit 01cc82ece091aa3bec4c07fdd6bc9e5135fca573)
36c85da3b8