[Dispatcher tests] Clean up parent-level Dispatcher tests.
[Dispatcher tests] Clean up parent-level Dispatcher tests.

A more thorough cleaning (removing <any>s, etc) probably depends
on https://github.com/palantir/plottable/issues/2968.

palantir/plottable,palantir/plottable,NextTuesday/plottable,palantir/plottable,NextTuesday/plottable,softwords/plottable,softwords/plottable,palantir/plottable,NextTuesday/plottable,softwords/plottable