docs: Stop using the function tag

gio/gactiongroup.c

@@ -64,7 +64,7 @@
  * with actions.  'Internal' APIs (ie: ones meant only to be accessed by
  * the action group implementation) are found on subclasses.  This is
  * why you will find - for example - g_action_group_get_action_enabled()
- * but not an equivalent <function>set()</function> call.
+ * but not an equivalent set() call.
  *
  * Signals are emitted on the action group in response to state changes
  * on individual actions.