Use or delete ZCPKG_PATH_LENGTH_BUDGET

[zyrolasting]

ZCPKG_PATH_LENGTH_BUDGET is currently dead, mainly because I wasn't sure how to use it.

I think it makes sense for use in a report where you:

1. Assume a given workspace directory
2. Find the longest path in the workspace
3. Subtract the length of the longest path from the path budget.

So if you say a workspace sits in a Windows C:\Users\John\Code directory, you can estimate if a workspace will create a path that exceeds Windows' default max path length (which is pretty short, and causes issues like microsoft/nodejstools#69).

I hesitate to implement this because it could just as easily be a package written for zcpkg. I'm partial to keeping it lean, but the only defense for putting in this feature is that zcpkg does make this problem possible.