Now that all backends pass in a list of acceptable DRM formats, that is used to
determine if the EGLConfig has an alpha channel or not. Therefore the
opaque_attribs and alpha_attribs are now useless, and we can remove the whole
config_attribs argument from the API.
gl_renderer_get_egl_config() uses an internal attrib list that matches at least
the union of the opaque_attribs and alpha_attribs matches.
Overall, behaviour should remain unchanged.
The new attribute array becomes variable in the future, so it is left
non-const.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>