fix(medications): drop the unused DoseUnitKey export

The shared dose-unit module exported a DoseUnitKey type alias that nothing
consumed, tripping the dead-code gate. Drop it; the const array is the
only export the wizard and formatDose need.

src/lib/medications/dose-units.ts

@@ -25,5 +25,3 @@ export const DOSE_UNIT_KEYS = [
   "pieces",
   "other",
 ] as const;
-
-export type DoseUnitKey = (typeof DOSE_UNIT_KEYS)[number];