unexpected multi-type 'allOff' references in runtime.lex.v2 spec

the generated specification contains unexpected 'allOf' references: https://github.com/APIs-guru/openapi-directory/blob/main/APIs/amazonaws.com/runtime.lex.v2/2020-08-07/openapi.yaml

this brakes openAPi client generators: such as swagger-codegen maven plugin for java.

I'll suggest a PR later on this days