Quieten nnir.el compilation

Quieten nnir.el compilation

* lisp/gnus/nnir.el (gnus-inhibit-demon, gnus-article-decode-hook):
Declare dynamic variables.
(nnir-request-group, nnir-retrieve-headers)
(nnir-request-move-article, nnir-request-update-mark)
(nnir-run-swish++, nnir-run-swish-e, nnir-run-namazu)
(nnir-run-notmuch, nnir-registry-action)
(nnir-request-create-group, nnir-request-delete-group)
(nnir-request-list, nnir-request-scan): Mark unused arguments.
(nnir-warp-to-article, nnir-run-imap, nnir-run-gmane)
(nnir-get-active): Remove unused local variables.