remove getAnonymousNodes() code path from getAllElements()

remove getAnonymousNodes() code path from getAllElements()

in fx68 and newer, there are no in-content bindings (i.e. those in .xul
about:-pages) left, and hardly any that are reachable via VimFx hints.
The only element with anonymous nodes that was reachable that way is the
(non-megabar) URL bar, which is better focused using 'o'.

The other now removed function, getBindingParent(), will have to stay;
otherwise custom elements (e.g. on bugs.chromium.org or the <xul:tree>
element on XUL-about:config) won't be properly clickable through hints.