public Stream<Trait> removedTraits() {
        return traitDiff.values()
                .stream()
                .filter(pair -> pair.getRight() == null)
                .map(Pair::getLeft);
    }
Gets a stream of removed traits.

@return Returns the traits that were removed.
smithy-diff/src/main/java/software/amazon/smithy/diff/ChangedShape.java