doc: remove stability from unreleased errors

[Trott]

Remove stability indicators from errors that only existed on the master
branch and are not in the release.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

[Trott]

These two errors are in the "Other error codes" section indicating they have never been released. They are listed here only because they had been on the master branch at some point. Not sure who to ping for reviews....

[jasnell]

If the error codes are not being used, they should just be removed entirely.

[Trott]

If the error codes are not being used, they should just be removed entirely.

I can't find where it's documented right now (so maybe it's not?) but my impression was that any error code that ever appeared in a release--even a nightly!--could never be removed from the documentation. In fact, I thought you were the one that originated that policy! But again, I can't find it anywhere, so maybe I'm wrong on all counts. (Maybe I'm confusing it with deprecation codes?)

Regardless, I'd be for removing unused error codes.

/ping @addaleax

[addaleax]

I don’t have a strong opinion, but I do like that we keep the error codes around that were released but removed in a later release.

[jasnell]

Released, then removed is one thing. There needs to be a section for defunct error codes if there isn't already. But if the code was never in a release and is never used, it should be removed.

[Trott]

Landed in 21005c3. I'll open a PR to remove these entirely now, but wanted to get the stability labels removed regardless in case that PR doesn't land.