doc: remove old system_errors

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

Fixes: https://github.com/nodejs/node/issues/26861
PR-URL: https://github.com/nodejs/node/pull/27037


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Signed-off-by: Beth Griggs <Bethany.Griggs@uk.ibm.com>