Do not issue empty list merge operations

mdsal-3.0.0 requires yangtools-2.1.0, which implies that lists in the datastore undergo automatic lifecycle, i.e. empty lists are disappearing and also non-present lists appear as needed.

This means that Binding Spec's inability to target lists is no longer a problem and binding-dom-adapter does not need to issue empty merges. Remove this code, reducing the number of operations binding performs, matching more closely DOM operations.