Obsolete and remove nmail-group-names-not-encoded-p
* lisp/gnus/nnmail.el (nnmail-group-names-not-encoded-p): Use make-obsolete-variable. (nnmail-split-incoming): Do not bind. * lisp/gnus/nnml.el (nnml-save-mail, nnml-active-number): Remove check. (nnml-request-group, nnml-request-expire-articles): Group name is already decoded, don't decode again.