I'm talking about this question: Why would IQF shrimp say "do not force thaw under running water"?
I don't think the "who" part of this question is helpful, so for now, I'm going to say it could've been any one of the mods. I think the "why" is perhaps worth answering, though, as a bit of insight into one of the general reasons mods delete comments.
sarge_smith: Are these already peeled shrimp?
Jeff Axelrod: @sarge_smith no, and I edited to clarify.
sarge_smith: According to your comment below, they are. Tails still on but the rest peeled is closer to peeled than not when handling. That said, the first part of MandoMando's answer is correct. the warning on the bag has nothing to do with food safety and every thing to do with product quality.
Jeff Axelrod: @sarge_smith yes, sorry, I spaced out and wrote no instead of yes.
Jeff actually deleted the first comment himself, presumably because it was incorrect. The other two comments were flagged as obsolete, and that's true: the issue of whether the shrimp are peeled is now addressed in the question. So the flags are valid, and mods can be expected to act accordingly. Jeff's last comment can also now reasonably be deleted; a mod would leave it there temporarily in order to make sure you saw it, but it is now also obsolete.
As the comments privileges page says, comments are in general temporary:
Comments are temporary "Post-It" notes left on a question or answer. They can be up-voted (but not down-voted) and flagged, but do not generate reputation. There's no revision history, and when they are deleted they're gone for good.
So it's to be expected that sometimes comments get removed. The goal is to keep the site tidy. When a future reader sees a question, they're going to start reading the page from top to bottom, so it's a service to them if they don't get sidetracked by obsolete comments. Ideally, a question is clear and complete, so that it doesn't need comments for clarification. Not all questions start that way, but the combination of making and deleting comments allows it to get there eventually. The site provides "obsolete" as one of the reasons to flag as a comment for, among others, situations like this one. Comments can also be flagged as rude/offensive, chatty, or off-topic; this serves a similar purpose.
I should also say that there are a lot of obsolete comments on the site; not all questions look like this one. I don't think any of the mods go hunting through for things to delete, but when things are flagged, we do address the flags.
I was the moderator who deleted the comments in the course of handling them. But as @Jefromi explained, this is pretty standard practice. Once a comment gets flagged, it is normally deleted unless is a very good reason not to (as opposed to answers which only get deleted if there is no other way around it).