[mutter] clutter: Remove clutter_set_windowing_backend()

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 033a771e8cdf6ac7c6e3eb31bd0dd6d427eccec4
Author: Adam Jackson <ajax redhat com>
Date:   Fri Mar 1 11:18:28 2019 -0500

    clutter: Remove clutter_set_windowing_backend()
    
    This is a choice imposed by mutter, not something you can usefully set
    from the config file.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/463

 clutter/clutter/clutter-backend-private.h |  2 --
 clutter/clutter/clutter-backend.c         | 55 -------------------------------
 clutter/clutter/clutter-backend.h         |  3 --
 clutter/clutter/clutter-main.c            | 11 -------
 4 files changed, 71 deletions(-)
---
diff --git a/clutter/clutter/clutter-backend-private.h b/clutter/clutter/clutter-backend-private.h
index 42d122890..50208c3ae 100644
--- a/clutter/clutter/clutter-backend-private.h
+++ b/clutter/clutter/clutter-backend-private.h
@@ -160,8 +160,6 @@ void                    _clutter_backend_reset_cogl_framebuffer         (Clutter
 
 void                    clutter_set_allowed_drivers                     (const char             *drivers);
 
-void                    clutter_try_set_windowing_backend               (const char             *drivers);
-
 G_END_DECLS
 
 #endif /* __CLUTTER_BACKEND_PRIVATE_H__ */
diff --git a/clutter/clutter/clutter-backend.c b/clutter/clutter/clutter-backend.c
index 2b9c3d1a1..d4b6a2d6b 100644
--- a/clutter/clutter/clutter-backend.c
+++ b/clutter/clutter/clutter-backend.c
@@ -1094,61 +1094,6 @@ clutter_wayland_set_compositor_display (void *display)
 }
 #endif
 
-/**
- * clutter_set_windowing_backend:
- * @backend_type: a comma separated list of windowing backends
- *
- * Restricts Clutter to only use the specified backend or list of backends.
- *
- * You can use one of the `CLUTTER_WINDOWING_*` symbols, e.g.
- *
- * |[<!-- language="C" -->
- *   clutter_set_windowing_backend (CLUTTER_WINDOWING_X11);
- * ]|
- *
- * Will force Clutter to use the X11 windowing and input backend, and terminate
- * if the X11 backend could not be initialized successfully.
- *
- * Since Clutter 1.26, you can also use a comma-separated list of windowing
- * system backends to provide a fallback in case backends are not available or
- * enabled, e.g.:
- *
- * |[<!-- language="C" -->
- *   clutter_set_windowing_backend ("gdk,wayland,x11");
- * ]|
- *
- * Will make Clutter test for the GDK, Wayland, and X11 backends in that order.
- *
- * You can use the `*` special value to ask Clutter to use the internally
- * defined list of backends. For instance:
- *
- * |[<!-- language="C" -->
- *   clutter_set_windowing_backend ("x11,wayland,*");
- * ]|
- *
- * Will make Clutter test the X11 and Wayland backends, and then fall back
- * to the internal list of available backends.
- *
- * This function must be called before the first API call to Clutter, including
- * clutter_get_option_context()
- *
- * Since: 1.16
- */
-void
-clutter_set_windowing_backend (const char *backend_type)
-{
-  g_return_if_fail (backend_type != NULL);
-
-  allowed_backends = g_strdup (backend_type);
-}
-
-void
-clutter_try_set_windowing_backend (const char *backend_type)
-{
-  if (allowed_backends == NULL)
-    clutter_set_windowing_backend (backend_type);
-}
-
 PangoDirection
 _clutter_backend_get_keymap_direction (ClutterBackend *backend)
 {
diff --git a/clutter/clutter/clutter-backend.h b/clutter/clutter/clutter-backend.h
index 93bd72b51..fde57d8f2 100644
--- a/clutter/clutter/clutter-backend.h
+++ b/clutter/clutter/clutter-backend.h
@@ -60,9 +60,6 @@ GType clutter_backend_get_type (void) G_GNUC_CONST;
 CLUTTER_EXPORT
 ClutterBackend *                clutter_get_default_backend             (void);
 
-CLUTTER_EXPORT
-void                            clutter_set_windowing_backend           (const char *backend_type);
-
 CLUTTER_EXPORT
 gdouble                         clutter_backend_get_resolution          (ClutterBackend             
*backend);
 
diff --git a/clutter/clutter/clutter-main.c b/clutter/clutter/clutter-main.c
index 07b8e9a2a..71ec0d80c 100644
--- a/clutter/clutter/clutter-main.c
+++ b/clutter/clutter/clutter-main.c
@@ -193,17 +193,6 @@ clutter_config_read_from_key_file (GKeyFile *keyfile)
   if (!g_key_file_has_group (keyfile, ENVIRONMENT_GROUP))
     return;
 
-  str_value =
-    g_key_file_get_string (keyfile, ENVIRONMENT_GROUP,
-                           "Backends",
-                           &key_error);
-  if (key_error != NULL)
-    g_clear_error (&key_error);
-  else
-    clutter_try_set_windowing_backend (str_value);
-
-  g_free (str_value);
-
   str_value =
     g_key_file_get_string (keyfile, ENVIRONMENT_GROUP,
                            "Drivers",