fix: improve test coverage, remove scope guards

[danyill]

Some small simplifications:

• Remove describe.only to run test suite and then fix treatment of Private elements.
• Remove scope test. We can assume our SCL file is valid and it's not testable.
• Remove nullish array coalescing, we never need this for these cases.
• Remove Private check, we never need this because we have already filtered out Private elements.

I'm just getting back to scl-lib after a hiatus so I'm not intending to be especially pedantic, so sorry if this is a bit annoying 😿

These changes bring our test coverage for removeIED.ts up to 💯%

[stee-re]

Wow! When I scanned over the changes, I thought to myself - no way - this is impossible!! But every single thing you found in removeIED was 100% spot on!! Thank you for making all of this better. I'm still embarressed that I let a "describe.only" get committed!!

[stee-re]

Thank you for all these improvements - REALLY appriciated!!!