doc: remove old errors_system_errors

[JungMinu]

• remove old errors_system_errors which partially predate the existence of the class, any useful information in it moved into the SystemError class docs
• outdent SystemError class docs to the same level as all the other classes

Checklist

• documentation is changed or added
• commit message follows commit guidelines

[nodejs-github-bot]

@JungMinu Sadly, an error occurred when I tried to trigger a build. :(

[BridgeAR]

Should we really remove the whole description? It still seems partially useful to me?

[JungMinu]

See #26861 for context

[sam-github]

Didn't see Ruben's comment because it was hidden/resolved. I agree with him.

[sam-github]

I think these two paragraphs, slightly edited, should be moved to be the description of class SystemError, because the information in them is still useful.

[sam-github]

This is intended to fix #26861, I believe. Could you edit the commit description to change it from:

remove old errors_system_errors, any useful information
in it moved into the SystemError class docs

to be punctuated and capitalized:

Remove ..
.... class docs.

Fixes: https://github.com/nodejs/node/issues/26861

[sam-github]

@JungMinu why did you close this? If it was to change the commit message, you can do that with git commit --amend, and then do a git push --force-with-lease, and the PR will be updated in place.

[JungMinu]

@sam-github I know that but was already in the middle of updating it in another PR, closing this PR