Removing SWT authentication handler

[mathewc]

Earlier in the year, I had already deactivated the SWT authentication handler (in this PR). Those changes have been fully released.

In this PR I'm just cleaning this dead code up now - removing the auth handler and supporting code. This handles incoming SWTs (no longer supported). I'll handle outbound SWTs in an upcoming PR. There are only 2 outbound calls SWTs are included on, and those can be controlled via hosting config. So for that, we'll do hosting config testing first, then follow up with code removal.

I will be backporting this to the in-proc branch, but no further.

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Removing SWT authentication handler #10675
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)