cogl: deprecates cogl_check_extension

OpenGL is an implementation detail for Cogl so it's not appropriate to
expose OpenGL extensions through the Cogl API.

Note: Clutter is currently still using this API, because it is still
doing raw GL calls in ClutterGLXTexturePixmap, so this introduces a
couple of (legitimate) build warnings while compiling Clutter.

cogl/driver/gles/cogl.c

@@ -32,31 +32,6 @@
 #include "cogl-context.h"
 #include "cogl-feature-private.h"
 
-gboolean
-cogl_check_extension (const gchar *name, const gchar *ext)
-{
-  gchar *end;
-  gint name_len, n;
-
-  if (name == NULL || ext == NULL)
-    return FALSE;
-
-  end = (gchar*)(ext + strlen(ext));
-
-  name_len = strlen(name);
-
-  while (ext < end)
-    {
-      n = strcspn(ext, " ");
-
-      if ((name_len == n) && (!strncmp(name, ext, n)))
-	return TRUE;
-      ext += (n + 1);
-    }
-
-  return FALSE;
-}
-
 gboolean
 _cogl_check_driver_valid (GError **error)
 {