Cleanup unused OAuth2 scheme from API

OAuth2 scheme in OpenBanking API is not used, instead request signing is used we need to fix that
```
securitySchemes:
BearerAuthOAuth:
description: |
Bearer Token.
type: http
scheme: bearer
accessCode:
type: oauth2
flows:
authorizationCode:
authorizationUrl: "http://example.com/oauth/auth"
tokenUrl: "http://example.com/oauth/token"
scopes:
write: allows modifying resources
read: allows reading resources
```