* lisp/erc/erc-backend.el: Use lexical-binding. Silence byte-compiler

* lisp/erc/erc-backend.el: Use lexical-binding. Silence byte-compiler

Use #' to quote functions.
(erc-server-delayed-reconnect): Remove unused arg `event'.
(erc-process-sentinel-2): Adjust accordingly.
Don't pass `err' to condition-case if we don't use it.
(define-erc-response-handler): Use add-hook rather than add-to-list.
(NICK): Use cl-pushnew rather than add-to-list.
(331): Remove unused var `topic'.
(352): Remove unused var `hopcount'.