refactor: autopush-common remove legacy autopush

[taddes]

Closes SYNC-4261

This will be somewhat more trivial in scope as SYNC-3451 will remove the dependencies and code related to some of these dependencies (usoto_core, rusoto_dynamodb, and serde_dynamodb)

[pjenvey]

There's a number of ApcErrorKind variants that are no longer used (solely by legacy autopush) that could be removed.

I'm not sure if there's an easy way to detect these other than removing all of them then checking where rustc complains

[taddes]

Great catch @pjenvey , I removed those referenced in autopush by cross referencing the old crate and did some compiler checks to make sure there were no issues. There was an unused Thread(Box<dyn Any + Send>) error that wasn't called anywhere that I took out, too.

[pjenvey]

@taddes I'm seeing even more unused variants!

Sorry to persist on this but this is a good time to remove all the unnecessary ones (and if enough are removed we might even consider removing ApcError itself in the future).

I've spotted PongTimeout and ExcessivePing as being from legacy autopush (the new autoconnect has their own versions of these), so there might be others as well.

[pjenvey]

Still seeing a couple here that could be removed such as the PongTimeout and ExcessivePing I mentioned

[taddes]

@pjenvey I think that accounts for all of the unused variants. BroadcastError, GeneralError, ConfigError, & PayloadError
 are all used externally directly, with the others covering errors using the From trait, so I left them be. Let me know if that seems sufficient. Thanks!

[pjenvey]

I think I'm also seeing the Json and Httparse variants unused, can you double check those?

[taddes]

Hm, might those need to remain for the status method?

[taddes]

Alright, got em @pjenvey !

[jrconlin]

🎉