Revert "[hack] don't recompute files with errors"

Summary: This reverts commit D1387289. There are cases when the
invariants listed don't actually hold, we need to think this through
more carefully.

Almost a clean revert -- one change to `serverTypeCheck` in D1390136
conflicted, pretty sure we can just nuke that change.

Reviewed By: @pikatchu

Differential Revision: D1401096