Remove the "ack" symlink

Doing it in two steps to not make "git log --follow" unhappy.

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$ git mv ack-standalone ack

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Merge branch 'move-ack'

* move-ack:
  $ git mv ack-standalone ack
  Remove the "ack" symlink

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ack: Updated to version 2.12, released on 2013-12-03

$ curl http://beyondgrep.com/ack-2.12-single-file >ack; chmod +x ack

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