test_thread.rb: remove garbage

* bootstraptest/test_thread.rb: remove a garbage line for debug.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46380 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bootstraptest/test_thread.rb

@@ -458,7 +458,6 @@ assert_equal 'ok', %q{
 
 assert_equal 'foo', %q{
   i = 0
-th2 = nil
   Thread.start {sleep 1; exit!}
   f = proc {|s, c| /#{c.call; s}/o }
   th2 = Thread.new {