Vestigial http2.error-handling dependency

[jeremyk-91]

@jkozlowski let me know that we apparently still depend on http2 error-handling (!), for some funky legacy compatibility with old http-remoting clients when attempting to acquire the Backup Lock (!!) when doing background sweep (!!!). We should remove this. Note that while I don't believe this code path is actually used, paths very close by are used, so a bit of caution is probably required.