refactor: cleanup now-unreferenced proto toolchain type

[alexeagle]

Follow-up to #2604, fixes a breaking change in v1.2.0-rc0

Note that this toolchain_type became unused in that PR. We leave behind an alias to make this a non-breaking change.

Verified in a downstream repo that requires the toolchain_type to register pre-built protoc: https://github.com/aspect-build/toolchains_protoc/pull/50/files

[aignas]

Thanks for the fix!

[aignas]

I meant something like https://github.com/bazelbuild/rules_python/blob/f2941df7562c4183c37d6ceeae23e7d390738d58/docs/BUILD.bazel#L182

[alexeagle]

Sure - @aignas to move things along faster please feel free to just click the "pencil" icon and make trivial edits like that as your own commits on my PR 😉
I do that for our contributors pretty frequently to spare the round-trip (unless the comment is something they might learn from)

[rickeylev]

I added the deprecation attr setting. It's annoying that the toolchain type is under a "private" directory. They should give a public access point for it.

Queued for merge. I'll cherry pick this into the 1.2 release.

[aignas]

Sure - @aignas to move things along faster please feel free to just click the "pencil" icon and make trivial edits like that as your own commits on my PR 😉 I do that for our contributors pretty frequently to spare the round-trip (unless the comment is something they might learn from)

I do it when I can and when I have my laptop with me. I am not doing it now not because I don't know how to or am unwilling, so no need to point it out. :)

In other words, everybody does as much as they can. :)