MARTE11 — Remove the TimedObservation stereotype

TimedObservation is an abstract stereotype that extends TimedElement without adding new features. It is sublassed by the concrete TimedDurationObservation and TimedInstantObservation. Given that it cannot be directly used, and for the sake of smplicity, removing the stereotype may be considered

Stereotype TimedObservation was created for consistency with the UML
Specification and considering that TimeExpression would refer to
TimedObservation directly without deciding on the actual specialization.
The stereotype can be removed with no harm. TimeExpression will refer to
(untimed) Observation instead. Even though the semantics is weakened, there is
no actual impact since the association between TimeExpression and Observation
is not actually serialized by any tool.
Though, it should be noted that TimedObservation cannot be removed from the
Domain View since it is actually used by DurationPredicate and TimePredicate.