dom-anchor-fragment is shipped as a UMD module which causes problems on
pages that declare a global function called `define` (see #479).

While we could fix the module, fragment anchoring is not very useful at
the moment. The client primarily anchors to the quote and uses other
anchors only as an optimization. The Wikipedia baseline tests changed in
this PR show how little value a fragment has on real websites.
Therefore, just remove support for generating and using fragment selectors.

This change should not cause anchoring regressions, as anchoring would
only have succeeded previously if the quote selector matched. Now it will just
fall through to anchoring using the range, position or quote selectors instead.

Fixes #479