remove contrib/magit-classic-theme.el

I very much doubt that anybody is using this because it is very
incomplete.  If you do use it please contact me.

The removal is done with the okay of the original author of this
file.

Makefile

@@ -3,7 +3,7 @@ EMACS=emacs
 PREFIX=/usr/local
 SYSCONFDIR=/etc
 ELS=magit.el magit-svn.el magit-topgit.el magit-stgit.el magit-key-mode.el magit-bisect.el magit-wip.el rebase-mode.el magit-blame.el
-ELS_CONTRIB=contrib/magit-simple-keys.el contrib/magit-classic-theme.el
+ELS_CONTRIB=contrib/magit-simple-keys.el
 ELCS=$(ELS:.el=.elc)
 ELCS_CONTRIB=$(ELS_CONTRIB:.el=.elc)
 DIST_FILES=$(ELS) Makefile magit.texi magit.info README.md magit.spec.in magit-pkg.el.in