Remove preload tests until review is complete.

These tests are great, but they were written against Presto and
test a bunch of things that are not in the spec. This is being fixed
in r/604 but until then it seems better to remove them since some of the
problems lead to instability in results.
Merge pull request #845 from w3c/jgraham/remove_preload

Remove preload tests until review is complete.