Simplify callback handling.
Simplify callback handling.

Follow-up r19260.

* subversion/bindings/swig/ruby/svn/fs.rb
  (Svn::Fs::Root#replay): Use nil instead of dummy callback Proc.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@859335 13f79535-47bb-0310-9956-ffa450edef68

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