Cleanup unused OAuth2 scheme from API

[valb3r]

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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