The change to provide public register/unregister methods in
AbstractHandlerMethodMapping assumed that a single method cannot be
mapped more than once. This is not the case with the MvcEndpoints and
EndpointHandlerMapping from Spring Boot which wrap one or more
non-web Endpoint types with an MvcEndpointAdapter in order to expose
them for use over the web. In effect Spring MVC sees a single handler
method mapped many times.
This change removes that assumption so rather than unregistering with
a HandlerMethod, which is not necessarily unique, the unregister method
now takes the actual mapping, which is the only thing that should actually
be unique.
Issue: SPR-11541
71683c5f8d