tools: remove unused GuessWordSize function

Apart from the fact that the implementation is not reliable,
GuessWordSize is not used anywhere in the codebase.

PR-URL: https://github.com/iojs/io.js/pull/1638


Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>