format: switch from CurrencyPipe to DecimalPipe

format: switch from CurrencyPipe to DecimalPipe

CurrencyPipe has no easy way of displaying the monetary amount
without a currency symbol, which means that currency amounts
display with a dollar sign -- which isn't a univeral assumption
for Evergreen.

Future work is indicated to (a) teach Evergreen a global flag
or a library setting for the system's base currency and (b) let
the format service be passed a currency code. Once both are in place,
CurrencyPipe can be restored.

Signed-off-by: Galen Charlton <gmc@equinoxOLI.org>