libgimpwidgets: move docs from template files to inline comments

but leave the template file for gimpstock there because its contents
would be too much for gimpstock.h.

libgimpwidgets/gimpoldwidgets.c

@@ -33,6 +33,17 @@
 #include "gimpoldwidgets.h"
 
 
+/**
+ * SECTION: gimpoldwidgets
+ * @title: GimpOldWidgets
+ * @short_description: Old API that is still available but declared
+ *                     as deprecated.
+ * @see_also: #GimpIntComboBox
+ *
+ * These functions are not defined if you #define GIMP_DISABLE_DEPRECATED.
+ **/
+
+
 /*
  *  Widget Constructors
  */