Remove any remaining support for requests to abstract endpoints like [base]/Resource

[lmsurpre]

Is your feature request related to a problem? Please describe.
In #2526 we added warnings for requests to "abstract" type endpoints like [base]/Resource.
Now I'd like to pull the trigger and remove that support altogether.

Describe the solution you'd like
have requests to [base]/Resource handled just like requests to [base]/bogus

Describe alternatives you've considered
keep supporting it in whatever way we do today

Acceptance Criteria

1. GIVEN a 5.0 version of IBM FhIR Server
   WHEN a request is made to [base]/bogus
   THEN it results in a 404 not found

Additional context
one such place is FHIRResource.checkType(String):

if (!ModelSupport.isConcreteResourceType(type)) {
            log.warning("Use of abstract resource types like '" + type + "' in FHIR URLs is deprecated and will be removed in a future release");
}

[d0roppe]

Error 404 issued with the text the "unknow" text is not a valid resource Closing issue.
The 404 is given for both 4.0 and 4.3 fhir versions