Revert "[ruby/fiddle] Fix a failing test (#13)"

This reverts commit 5ebb0d50f6.

test/fiddle/test_import.rb

@@ -149,18 +149,7 @@ module Fiddle
     end
 
     def test_no_message_with_debug
-      # disable all Ruby environment variables
-      orig_RUBYOPT, ENV['RUBYOPT'] = ENV['RUBYOPT'], nil
-      orig_RUBYLIB, ENV['RUBYLIB'] = ENV['RUBYLIB'], nil
-
-      # load development fiddle instead of bundled one
-      libdir = File.expand_path('../../../lib', __FILE__)
-      ENV['RUBYLIB'] = libdir if File.file?(File.join(libdir, "fiddle/import.rb"))
-
       assert_in_out_err(%w[--debug --disable=gems -rfiddle/import], 'p Fiddle::Importer', ['Fiddle::Importer'])
-    ensure
-      ENV['RUBYLIB'] = orig_RUBYLIB
-      ENV['RUBYOPT'] = orig_RUBYOPT
     end
   end
 end if defined?(Fiddle)