[MINOR] Make appsess{,ion}_refresh static

[MINOR] Make appsess{,ion}_refresh static

apsession_refresh() and apsess_refressh are only used inside apsession.c
and thus can be made static.

The only use of apsession_refresh() is appsession_task_init().
These functions have been re-ordered to avoid the need for
a forward-declaration of apsession_refresh().