Remove lib-src/grep-changelog

Ref: http://lists.gnu.org/archive/html/emacs-devel/2014-12/msg00145.html

* lib-src/grep-changelog: Remove file.

* lib-src/Makefile.in (INSTALLABLE_SCRIPTS): Remove.
(all, install, uninstall): Remove INSTALLABLE_SCRIPTS.

* doc/man/grep-changelog.1: Remove file.

* make-dist: No more lib-src/grep-changelog.

* INSTALL: No longer mention grep-changelog.

* admin/quick-install-emacs (PUBLIC_LIBSRC_SCRIPTS): Remove, and all uses.

* admin/authors.el (authors-valid-file-names): Add grep-changelog.

* etc/NEWS: Mention this.