TODO:
- store, instead of just skip over, nu5 transaction fields
- add relevant nu5 fields to CompactBlock
- restore disabled V4 unit tests
- add V5 test vectors to unit tests
The reason most of the V4 transaction and block unit tests are removed
is that they used V3 transactions, which lightwalletd never sees in
production, since lightwalletd starts at Sapling activation (which has
V4 transactions). So these tests were always wrong, in a way. This
commit simplifies the parsing code by removing support for V3 (since it
was never needed). The tests need to be updated to V4, but we'll do
that in a later PR.
ddf3781a60