CellRenderer|Editable: Don't @See_also subclasses

The documentation knows that from the inheritance hierarchy, without us
having to manually duplicate that info here. Link to each other instead.

gtk/gtkcelleditable.c

@@ -19,7 +19,7 @@
  * SECTION:gtkcelleditable
  * @Short_description: Interface for widgets that can be used for editing cells
  * @Title: GtkCellEditable
- * @See_also: #GtkEntry, #GtkCellRenderer
+ * @See_also: #GtkCellRenderer
  *
  * The #GtkCellEditable interface must be implemented for widgets to be usable
  * to edit the contents of a #GtkTreeView cell. It provides a way to specify how

gtk/gtkcellrenderer.c

@@ -29,7 +29,7 @@
  * SECTION:gtkcellrenderer
  * @Short_description: An object for rendering a single cell
  * @Title: GtkCellRenderer
- * @See_also: #GtkCellRendererText, #GtkCellRendererPixbuf, #GtkCellRendererToggle
+ * @See_also: #GtkCellEditable
  *
  * The #GtkCellRenderer is a base class of a set of objects used for
  * rendering a cell to a #cairo_t.  These objects are used primarily by