Remove macOS (ARM) builders and build statuses

[daveverwer]

From #307 (comment)

(as an aside, at some point we should drop the ARM distinction and convert our builders to ARM only - faster, and less complexity overall)

It's best to discuss this separately from that comment so splitting it out into a new issue.

I think this is a good idea, but before we do it we should just have a quick look at how many packages differ between macOS (Intel) and macOS (ARM). We originally implemented this so we could check for ARM incompatibilities so we should make sure we're not losing too much valuable information before dropping it.

That said, ARM compatibility in your package is very much a requirement these days and it's not going away so if a few packages start showing macOS failures when we do this, that's fine since they'd likely not be usable in the real world anyway.