Remove deprecated `rake license_finder` task and railtie

The `rake license_finder` task is being removed for the 1.0 release, as promised since the 0.8.0 release.  As such, it will no longer be automatically included in Rails projects.

As the deprecation warnings suggested, if you were using `rake license_finder`, you should switch to the `license_finder` command line utility.  See `license_finder help` for additional commands and documentation.

This finishes Tracker chore [Remove rake](https://www.pivotaltracker.com/story/show/68538776)