PS: Revert extraction of code found via PSModulePath

[MathiasVP]

I want to handle implicit importing somewhat differently than what I did in #132. So for now I'll revert it.

• The first commit is a revert of PS: #132 follow-up #133 - except that I'm keeping extraction of .psd1 files
• The second commit is a revert of PS: Extract source files found via PSModulePath #132 - except that I'm keeping the upgrade and downgrade scripts
• The third commit is fixes a small bug in the upgrade script generator. Previously, it was relying on being run only from the github/codeql repo. I've fixed up the script so that it works on the Microsoft repo.
• The final commit modifies the upgrade and downgrade script to be compatible with the revert in the second commit.

Thanks for all the feedback so far, @dilanbhalla!