lib: Remove unnecessary TODO comments

[pgeiss]

Original committer (@trevnorris) stated they were safe to remove in issue comments.
Ref: Issue #4642

PS: I want to work more on the TODOs in 4642 (and, you know, actually fix things). I'm assuming I should direct questions if I have any there? It has a 'mentor-available' tag.

[Trott]

LGTM

The mentor who is available is probably @Fishrock123. (I'm inferring this from the fact that he's the one that added the mentor-available tag.) But yes, directing questions about #4642 to that actual issue is definitely the thing to do. I'm happy to help too, at least on areas of the code where I feel comfortable. And there are probably others too. If you want to try as many venues as possible, you can also try asking in the #node-dev IRC channel.

[pgeiss]

Rebased on latest master.

[cjihrig]

Thanks! Landed in 83d2b77. A full CI run isn't necessary for removing a few comments, but I did run the tests locally as a sanity check.

[rvagg]

Thanks for finding a place to contribute @pgeiss, it looks like this is your first commit in core, if so, welcome on board! I hope you can find other places to make an impact.