glamor: Drop stale comment.

The old Xephyr codebase was using the GL window system framebuffer for
the screen pixmap, but that meant you couldn't texture from it to do
operations sourcing from the screen, so in the version that landed I
instead had the screen just be a plain texture.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Keith Packard <keithp@keithp.com>

glamor/glamor_render.c

@@ -962,10 +962,6 @@ glamor_composite_choose_shader(CARD8 op,
             glamor_fallback("source == dest\n");
         }
         if (source_pixmap_priv->base.gl_fbo == GLAMOR_FBO_UNATTACHED) {
-            /* XXX in Xephyr, we may have gl_fbo equal to 1 but gl_tex
-             * equal to zero when the pixmap is screen pixmap. Then we may
-             * refer the tex zero directly latter in the composition.
-             * It seems that it works fine, but it may have potential problem*/
 #ifdef GLAMOR_PIXMAP_DYNAMIC_UPLOAD
             source_status = GLAMOR_UPLOAD_PENDING;
 #else