Revert "More precise complex :host selectors" - not needed anymore

With the recent updates to the shadow DOM-related CSS rules, :host(X) will only match if X is on the :host itself, so :host(X:host) becomes unnecessary (before, :host(X) would match if the :host or any of its ancestors had X).
Merge pull request #1373 from ussuri/more-precise-host-selectors

Revert "More precise complex :host selectors" - not needed anymore