Remove list of Vaadin elements about vaadin-usage-statistics

[web-padawan]

Currently, for Polymer 3 the global Vaadin namespace does not contain references to the components classes.

One possible solution:

1. Use vaadin-element-mixin for following components:

• Lumo: https://github.com/vaadin/vaadin-lumo-styles/blob/f8a592226bf0fe7faf6ab20868d24c755fb48b6d/version.html#L8
• Material: https://github.com/vaadin/vaadin-material-styles/blob/3fcc14857ca75f6c898968f28bfac86ee627fa0f/version.html#L8
• Router: https://github.com/vaadin/vaadin-router/blob/82e6262becfb24a147ead5f2b89c31350130e437/src/router-meta.js#L6

2. Update the ElementMixin to use static finalize() and add the static get is() getter value back to Vaadin namespace, e. g. to Vaadin.registrations similarly to how Polymer does that: https://github.com/Polymer/polymer/blob/0bf1e60c157b9ecdf56b6e308aeaea16d34ee04b/lib/mixins/element-mixin.js#L694