Remove version file to align with the single-file rule

One of trollop's features is to be a single file, so you are
not required to use as a gem.  The version file being
separate breaks that rule.

See https://github.com/ManageIQ/trollop/blob/master/README.md#features

Fixes #21
Merge pull request #22 from Fryguy/remove_version_file

Remove version file to align with the single-file rule