public Stream<Pair<String, Node>> removedMetadata() {
        return oldModel.getMetadata()
                .entrySet()
                .stream()
                .filter(entry -> !newModel.getMetadata().containsKey(entry.getKey()))
                .map(entry -> Pair.of(entry.getKey(), entry.getValue()));
    }
Gets all removed metadata.

<p>Each Pair returned contains the name of the metadata key on
the left of the Pair and the metadata value on the right.

@return Returns a stream of removed metadata.
smithy-diff/src/main/java/software/amazon/smithy/diff/Differences.java