[ruby/irb] Clear temporary directories

(https://github.com/ruby/irb/pull/894)

https://github.com/ruby/irb/commit/dc0dd25a39

test/irb/test_history.rb

@@ -27,6 +27,7 @@ module TestIRB
       ENV["IRBRC"] = @backup_irbrc
       Encoding.default_external = @backup_default_external
       $VERBOSE = @original_verbose
+      FileUtils.rm_rf(@tmpdir)
     end
 
     class TestInputMethodWithRelineHistory < TestInputMethod