RubySpec: fix bad spec defining X on Object.
RubySpec: fix bad spec defining X on Object.

* It caused an error as X might already be defined,
  such as by the lambda spec in language.
* Also see, as alternatives:
  https://github.com/jruby/jruby/commit/5b1fad2b0d6046f2ede26a83d24a8ae2f494c356
  https://github.com/anthonycrumley/rubyspec/commit/b7037e14e475b806a0daca0d3c5c11491c1387c9

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