glx: Pull use_x_font out of the context vtable

The client-side implementation of this operates entirely in terms of the
GL and X client APIs. There's nothing DRI-specific about it, evidenced
by apple and windows using it unchanged. Save a little code size by
handling the direct/indirect difference directly.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9690>

src/glx/dri2_glx.c

@@ -1047,7 +1047,6 @@ static const struct glx_context_vtable dri2_context_vtable = {
    .unbind              = dri2_unbind_context,
    .wait_gl             = dri2_wait_gl,
    .wait_x              = dri2_wait_x,
-   .use_x_font          = DRI_glXUseXFont,
    .bind_tex_image      = dri2_bind_tex_image,
    .release_tex_image   = dri2_release_tex_image,
    .get_proc_address    = NULL,