rbinstall.rb: remove unused variable

* tool/rbinstall.rb: $vcs is no longer used since r46513.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47247 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/rbinstall.rb

@@ -19,17 +19,10 @@ require 'optparse'
 require 'optparse/shellwords'
 require 'ostruct'
 require 'rubygems'
-require_relative 'vcs'
 
 STDOUT.sync = true
 File.umask(0)
 
-begin
-  $vcs = VCS.detect(File.expand_path('../..', __FILE__))
-rescue VCS::NotFoundError
-  $vcs = nil
-end
-
 def parse_args(argv = ARGV)
   $mantype = 'doc'
   $destdir = nil