Revert "Add magic comment US-ASCII for Ruby2.0.0"

This reverts commit 7c3194e69d8e49b7d32ba89f5a37d37ef3577f1d.

This is not correct solution
Add ASCII-8BIT option to regexp encoding

This does not change behavior in signet, but fixes strange syntax
error in google-api-ruby-client:
https://travis-ci.org/google/google-api-ruby-client/jobs/4052360
Merge pull request #10 from sanemat/fix/invalid-regex-encoding

Fix invalid regex encoding