[session] move context manager logic in the hook controls context manager
The `init_hooks_mode_categories` and `reset_hooks_mode_categories` have no other
user that the context manager itself. Having dedicated public function is not
useful.
Upstream Author:
%(author)s <%(author-email)s>
Copyright:
Copyright (c) %(year)s %(author)s.
%(author-web-site)s -- mailto:%(author-email)s