Remove option --code which has been broken since 2018

[matteius]

Remove option --code which has been broken since 2018

Issue description

Our code in pipenv has been passing a boolean for a path value and silently swallowing sine 2018 for this code path. The intention of the code path is to generate a requirements.txt from inspecting the project imports. To do this, it uses pipreqs which has not been well maintained and contains a mapping of project names where the imports don't match the project name -- which is many projects these days. I find the mapping file is largely incomplete and the CLI tool which can generate the requirements.txt is largely incomplete for the basic test projects I have tried this functionality on. See also:

• pipreqs future bndr/pipreqs#252
• https://github.com/bndr/pipreqs/blob/master/pipreqs/mapping

The Fix

Rather than try to fix this under documented and broken feature, I believe it is time to remove it. There are already better ways to generate a Pipfile from a requirements.txt and a requirements.txt from the Pipfile.lock. It would be more than a matter than passing the path in to fix it in, because the method we call also raises exception if it cannot resolve a single dependency which is likely.

Recommendation: If someone needs to generate a requirements.txt using pipreqs they can just install pipreqs and use their CLI to get started.

We do not need to continue vendoring it into pipenv, which will also allow us to drop yarg vendored dependency as well.