JSON makes no distinction between numbers and reals, and our code
doesn't need to do so either.
This removes VREAL, as well as its specific post-processing in
`UniValue::write`. Non-monetary amounts do not need to be forcibly
formatted with 8 decimals, so the extra roundtrip was unnecessary
(and potentially loses precision).
Zcash: cherry-picked from commit 7650449a6777710cf818d41862626164da0cd412
Left over from 2aee461930
d101d7b8e6