pkgs/pkcs7: Fix python library installation

[henrirosten]

This change is an attempt to fix pkcs7 python library installation.

This change fixes (or attempts to fix) the following problems:

• pkcs7 apparently depends on disttools package from https://github.com/jeppeter/disttools. The disttools isn't available in nixpkgs, nor is it packaged by the ci-test-automation flake. We would have to package it here, or break the dependency. The change done in this PR breaks the dependency, as it seems the package disttools is only needed for debugging. Therefore, this change simply removes the content from _ init_debug _.py that's between the tags ##importdebugstart and ##importdebugend.
• Before the changes from this PR, the pkcs7 library could be imported, but the library contents was empty. The reason was, the package name __init_debug__.py is not valid. This PR renames the pkcs7 __init_debug__.py to __init__.py to make the import work correctly. I doubt the earlier version of the pkcs7 library - as imported in this flake - has ever worked. For more details, see this article.