Review fixes: a missed passphrase change follows at the next backup, a key from before 1.1.0 counts as used, schedules edited in their own time zone

- A location that a passphrase change could not reach gets it at its next backup
- A key from before 1.1.0 is never replaced as an unused one
- An unreadable settings file on a location is told apart from a missing one
- A schedule is shown and saved in the zone it was saved in
- Saving an unchanged schedule keeps its moment; --timezone needs a schedule
- Schedule coverage uses the time the backup began reading its data
- Tests: catch-up scenario, upgrade test restores the new file, autumn clock change

src/format.js

@@ -26,30 +26,3 @@ export function formatSize(bytes) {
 	}
 	return i === 0 ? `${b} B` : `${b.toFixed(1)} ${units[i]}`
 }
-
-/**
- * A time of day "HH:MM" in zone `from`, as "HH:MM" in zone `to`, at today's offsets.
- *
- * @param {string} hhmm the time
- * @param {string} from IANA zone it is in
- * @param {string} to IANA zone to show it in
- * @param {Date} now the day to convert on (today)
- * @return {string}
- */
-export function toZone(hhmm, from, to, now = new Date()) {
-	const [h, m] = hhmm.split(':').map(Number)
-	const parts = (zone, date) => Object.fromEntries(new Intl.DateTimeFormat('en-GB', {
-		timeZone: zone, hourCycle: 'h23', year: 'numeric', month: '2-digit', day: '2-digit', hour: '2-digit', minute: '2-digit',
-	}).formatToParts(date).map((p) => [p.type, p.value]))
-	const offsetAt = (at) => {
-		const seen = parts(from, new Date(at))
-		return Date.UTC(+seen.year, +seen.month - 1, +seen.day, +seen.hour, +seen.minute) - at
-	}
-	const today = parts(from, now)
-	const wall = Date.UTC(+today.year, +today.month - 1, +today.day, h, m)
-	// the offset at the wall time itself: on a day the clocks change it differs from the one at
-	// midnight, so it is looked up a second time at the moment found first
-	const at = wall - offsetAt(wall - offsetAt(wall))
-	const there = parts(to, new Date(at))
-	return `${there.hour}:${there.minute}`
-}