AWS: Avoid warning about native extensions for unf gem

[floehopper]

• Consider avoiding warning about native extensions for unf gem
  • I have successfully used docker run -v `pwd`:`pwd` -w `pwd` -i -t lambci/lambda:build-ruby2.5 bundle install --path vendor/bundle to achieve this, but this seems like overkill given the lack of properly compile extensions isn't actually causing a problem
  • A better solution might be to avoid the indirect dependency on the unf gem; see this PR and the documentation for String#unicode_normalize for further details

[floehopper]

This was resolved in ff86d0c by no longer using the rest-client gem which is what depended on the unf gem. Closing.