Make some erc function aliases obsolete

Make some erc function aliases obsolete

* lisp/erc/erc-networks.el (erc-current-network):
* lisp/erc/erc-join.el (erc-autojoin-channels-delayed):
* lisp/erc/erc-backend.el (erc-server-setup-periodical-ping)
(erc-server-send-ping, erc-server-send-queue):
* lisp/erc/erc-autoaway.el (erc-autoaway-reestablish-idletimer)
(autoaway): Adjust callers.

* lisp/erc/erc-compat.el (erc-with-selected-window)
(erc-cancel-timer, erc-make-obsolete)
(erc-make-obsolete-variable): Make these aliases obsolete.