mesa: remove gl_texture_object references from glPush/PopAttrib stack

mesa: remove gl_texture_object references from glPush/PopAttrib stack

I don't see why this is needed and it's not used anywhere.
As long as apps don't call glDeleteTextures, nothing will release them.
And even if they do, we don't use the saved textures anywhere.

Also, BindTexture will fail for deleted textures anyway, so they can't be
popped. The existing code already binds the Name that was saved, not
the texture object that was saved.

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6946>