Remove cpython from the last ordered group

[pacostas]

!! Merge After !!

• Revert "Requiring python during build time in case is not available on the build image" node-engine#1337

Summary

Based on this discussion paketo-buildpacks/node-engine#1329 this PR removes the cpython from the last ordered group, as cpython can only be included from npm-install, therefore there is no such scenario anymore of another buildpack including it except npm-install

Use Cases

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).