clutter: Drop cairo_clear helper

It is used once in gnome-shell, so it is better to just move it content
there.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3086>

clutter/clutter/clutter-cairo.c

@@ -1,50 +0,0 @@
-/*
- * Clutter.
- *
- * An OpenGL based 'interactive canvas' library.
- *
- * Copyright (C) 2012 Intel Corporation
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library. If not, see <http://www.gnu.org/licenses/>.
- */
-
-/**
- * SECTION:clutter-cairo
- * @Title: Cairo integration
- * @Short_Description: Functions for interoperating with Cairo
- *
- * Clutter provides some utility functions for using Cairo.
- */
-
-#include "clutter/clutter-build-config.h"
-
-#include "clutter/clutter-cairo.h"
-#include "clutter/clutter-color.h"
-
-/**
- * clutter_cairo_clear:
- * @cr: a Cairo context
- *
- * Utility function to clear a Cairo context.
- */
-void
-clutter_cairo_clear (cairo_t *cr)
-{
-  cairo_save (cr);
-
-  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
-  cairo_paint (cr);
-
-  cairo_restore (cr);
-}

clutter/clutter/clutter-cairo.h

@@ -47,7 +47,4 @@ G_BEGIN_DECLS
 #define CLUTTER_CAIRO_FORMAT_ARGB32     (COGL_PIXEL_FORMAT_ARGB_8888_PRE)
 #endif
 
-CLUTTER_EXPORT
-void    clutter_cairo_clear             (cairo_t               *cr);
-
 G_END_DECLS

clutter/clutter/meson.build

@@ -110,7 +110,6 @@ clutter_sources = [
   'clutter-blur-effect.c',
   'clutter-box-layout.c',
   'clutter-brightness-contrast-effect.c',
-  'clutter-cairo.c',
   'clutter-canvas.c',
   'clutter-child-meta.c',
   'clutter-click-action.c',