Retire the WSSE AtomPub authentication mode

[snoopdave]

Roller's AtomPub endpoint supports a WSSE digest authentication mode that is no
longer used and is not maintained. This change removes it rather than carrying
it forward.

What changed

• Remove wsse from the AtomPub authentication dispatch and delete the WSSE
  parser/generator utility, which has no other production caller.
• Keep AtomPub and its supported authentication modes intact.
• Fail closed when an existing installation still has
  webservices.atomPubAuth=wsse (or any other unsupported value); never silently
  reinterpret that value as Basic authentication.
• Remove WSSE from the administrator-facing AtomPub authentication labels.
• No persistence manager, entity, table, schema migration, cache, or cluster
  coordination is required.

Tests

• With webservices.atomPubAuth=wsse, a request stays unauthenticated and does
  not fall back to Basic authentication.
• No production code or administrator-facing label references WSSE.
• The application compiles on JDK 11 and existing AtomPub authentication tests
  pass.