Core: Remove the newly introduced global hooks until we have consensus

Between locating the hooks in `QUnit` or `QUnit.config` and making them
simple setters and callback lists (like QUnit.done et al) and upcoming
plans for nested suites, we decided not to release this feature, for now.

I'm keeping the abstractions for hooks in place, so it should be trivial
to bring this back in whatever form we decide on later.

Effectively reverts 5ee31a083af3b17187f90cde54885bcc46d3dd8f and follow-up
commits.

Fixes #665
Ref #633
Ref #635
Ref #647