Remove defunct custos services

[nuwang]

The custos service is no longer maintained and therefore, both the custos auth provider and the custos vault are now defunct. This PR removes code that relies on these services.

These are some preliminary changes required to address: #20789

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[bgruening]

Thanks @nuwang for working on this!

[nsoranzo]

Close in favour of #21234 ?

[nuwang]

Close in favour of #21234 ?

The only reason to keep this around would be to make it easier to review. PR #21234 is based off this branch.