KERML_ — Eliminate EndFeatureMembership and ParameterMembership from abstract syntax

The KerML abstract syntax defines EndFeatureMembership, ParameterMembership, and ReturnParameterMembership.

These concepts do not add additional semantics to the model, as the same can be expressed using FeatureMembership with the appropriate Feature::isEnd and Feature::direction values on owningFeature.

Abstract syntax users (implementors and SysML v2 API users), are confused about which type of membership to use.

Proposal:
Eliminate EndFeatureMembership and ParameterMembership from the abstract syntax.

These modeling aspects are fully covered by Feature::isEnd and Feature::direction.