Conform to OAS3 unconditionally to satisfy swagger

[joostd]

Swagger complains about errors in our OpenAPI 3.0 Webauthn Schema

• for /v1/user on line 124

Semantic error at paths./v1/user.delete.requestBody
DELETE operations cannot have a requestBody.

• for /v1/user/credentials on line 203
  

Semantic error at paths./v1/user/credentials.delete.requestBody
DELETE operations cannot have a requestBody.

Swagger seems to have started to raise errors to conform to OAS3.
Their documentation states:

"GET, DELETE and HEAD are no longer allowed to have request body because it does not have defined semantics as per RFC 7231."

Although the OAS3 specs say:

"requestBody is permitted but does not have well-defined semantics and SHOULD be avoided if possible."

Do we need to change this in order to conform unconditionally?

[dmennis]

DELETE - /v1/user/credentials/{credentialId}