libgimp: clean comment.

I am unsure about the previous commit (see MR !2568), though it should
not be hurtful either. At least though, let's not leave duplicate
comments. So merging the 2 comments and making the remaining text a bit
more technically correct.

libgimp/gimp.c

@@ -1179,10 +1179,6 @@ _gimp_config (GPConfig *config)
                 "application-license", "GPL3",
                 NULL);
 
-  /* XXX Running gegl_init() before gegl_config() is not appreciated by
-   * GEGL and generates a bunch of CRITICALs.
-   */
-
   g_clear_object (&_check_custom_color1);
   _check_custom_color1 = gegl_color_new (NULL);
   pixel = g_bytes_get_data (config->check_custom_color1, &bpp);

libgimp/gimpplugin.c

@@ -290,16 +290,14 @@ gimp_plug_in_class_init (GimpPlugInClass *klass)
 
   g_object_class_install_properties (object_class, N_PROPS, props);
 
-  /* GIMP uses GeglColor so GEGL must be init.
-   * GEGL depends on BABL so it must be init.
-   *
-   * XXX Usually would call gegl_init which calls babl_init.
-   * But when call gegl_init before gegl_config,
-   * GEGL loads its libraries (also called plugins) twice
-   * and GObject throws CRITICAL re multiple register of GTypes
-   * "Two different plugins tried to register".
-   * See related XXX comment in libgimp/gimp.c
-   * See gegl#427
+  /* libgimp creates GeglColor-s in _gimp_config(), which requires at
+   * least babl to be initialized.
+   * We don't call gegl_init() because gegl_config() does not appreciate
+   * being called after, which generates a bunch of CRITICALs (see
+   * commit b06fe36970c and gegl#427).
+   * Therefore gegl_init() still needs to be called manually by plug-ins
+   * if necessary (it is called by gimp_ui_init() too, but this only
+   * applies to GUI plug-ins).
    */
   babl_init ();
 }