Remove support for `rake license_finder` task.

The `rake license_finder` task is being removed for the 1.0 release, as
promised since the 0.8.0 release.

If this causes you problems, switch to using the `license_finder`
command line utility.  See `license_finder help` for additional commands
and documentation.
Remove reference to file that no longer exists
Merge pull request #79 from mainej/remove-deprecated-rake-task-and-railtie

Remove deprecated `rake license_finder` task and railtie