Correct some type checking issues with referrer trimming

[kzar]

The argumentsObject and referrer trimming code were failing TypeScript
linting, so linting was disabled for those files. Let's fix the
problems and enable TypeScript linting again for them.

Reviewer: @jonathanKingston

Steps to test this PR:

Automated tests:

• Unit tests
• Integration tests

Reviewer Checklist:

• Ensure the PR solves the problem
• Review every line of code
• Ensure the PR does no harm by testing the changes thoroughly
• Get help if you're uncomfortable with any of the above!
• Determine if there are any quick wins that improve the implementation

PR Author Checklist:

• Get advice or leverage existing code
• Agree on technical approach with reviewer (if the changes are nuanced)
• Ensure that there is a testing strategy (and documented non-automated tests)
• Ensure there is a documented monitoring strategy (if necessary)
• Consider systems implications

[jonathanKingston]

No real issues just two discussion points 👍🏻

Edit: one discussion point because neither are side are great and I see why TS was sad :).