[ruby/digest] Remove obsolete test runner [ci skip]

This file is platform dependent, outdated and already not working.
Use `rake` instead.

https://github.com/ruby/digest/commit/a2a917dc71

ext/digest/test.sh

@@ -1,30 +0,0 @@
-#!/bin/sh
-#
-# $RoughId: test.sh,v 1.5 2001/07/13 15:38:27 knu Exp $
-# $Id$
-
-RUBY=${RUBY:=ruby}
-MAKE=${MAKE:=make}
-CFLAGS=${CFLAGS:=-Wall}
-
-${RUBY} extconf.rb --with-cflags="${CFLAGS}"
-${MAKE} clean
-${MAKE}
-
-for algo in md5 rmd160 sha1 sha2; do
-    args=--with-cflags="${CFLAGS}"
-
-    if [ $WITH_BUNDLED_ENGINES ]; then
-	args="$args --with-bundled-$algo"
-    fi
-
-    (cd $algo &&
-	${RUBY} extconf.rb $args;
-	${MAKE} clean;
-	${MAKE})
-    ln -sf ../../$algo/$algo.so lib/digest/
-done
-
-${RUBY} -I. -I./lib ../../test/digest/test_digest.rb
-
-rm lib/digest/*.so