cogl: Remove CoglBool, use gboolean instead

This basically reverts commit 54735dec, which tried to avoid the
GLib-defined types in favor the standard C ones. One exception to this
is the bool type, for which the commit introduces a new type CoglBool.

Let's just get rid of this type in favor of having consistency with the
GLib types. Note by the way that neither CoglBool nor gboolean (which
has a size of `int`) are completely compatible with bool (size `char`).

https://gitlab.gnome.org/GNOME/mutter/merge_requests/321

cogl/cogl/cogl-attribute-buffer.h

@@ -139,7 +139,7 @@ cogl_attribute_buffer_new (CoglContext *context,
  * Since: 1.4
  * Stability: Unstable
  */
-CoglBool
+gboolean
 cogl_is_attribute_buffer (void *object);
 
 G_END_DECLS