A conformance requirement on a concrete type parameter is redundant if the
concrete type conforms to the protocol.
The replacement path for the conformance rule is based on a concrete
conformance rule introduced by the property map. Since the concrete
conformance rule is not associated with a requirement ID, this would
normally muffle the redundancy warning, because we don't want to
suggest removing a rule that depends on a non-redundant, non-explicit
rule.
However, concrete conformance rules don't actually appear in the
minimal signature, so skip them when computing the set of non-redundant,
non-explicit rules to ensure that the original conformance requirement
is still diagnosed as redundant.
