feat(swingset)!: make dynamic vats unmetered by default

[warner]

When #3308 lands, the definition of "metering" will change. Previously, a
"metered dynamic vat" just meant that 1: each crank was limited to some fixed
amount of computrons, and 2: the low-level deliveryResult included the
number of computrons consumed by that delivery (but nobody paid attention to
the value).

In the new system, metering requires a Meter: an object with a remaining
capacity, which is deducted by the consumption of each delivery. Each metered
vat is associated with (exactly one) Meter. The presence of a Meter still
implies a per-crank limit: unmetered vats do not have a per-crank limit
either.

Previously, all dynamic vats were metered by default. Since the new metering
needs a Meter, it would be awkward to retain this default: we'd have to
allocate a new Meter during createVat without the caller's awareness, and
then there would be nobody to pay attention to it (or refill it when it runs
low).

So this commit changes the default to "false". Dynamic vats will be
unmetered (neither per-crank limits nor cumulative limits) by default.
Callers who want to retain the per-crank limits should add metered: true to
their createVat options. Such callers will need to create a Meter object
once #3308 is done.

The commit also updates swingset metering tests to add metered: true.

refs #3308

[FUDCo]

Could've been worse.