Refactor NumberInput without allowEmpty

- Delete all uses of allowEmpty={true} (that's now the default case)
- Account for all cases of allowEmpty={false} (which was easy b/c they all had implicit placeholders anyway)
- Update functions so wherever allowEmpty was used, it's now set as true
- Alter comments so that they are still relevant
- Refactor getValue without numberFromString

Test Plan: nothing should have changed

Auditors: jack