test_jit.rb: remove unnecessary require

At first I was going to check the name of `RbConfig::CONFIG['CC']` and
use shellwords for it, but I decided not to do so.

Thus removing obsoleted require in r62307.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62309 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_jit.rb

@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 require 'test/unit'
-require 'shellwords'
 
 # Test for --jit option
 class TestJIT < Test::Unit::TestCase