These functions and associated tests are being removed because nothing
depends on them and they end up creating a dependency on
blockchain/stake package, which is not desirable.
Putting the test code in the same package makes it easier for forks
since they don't have to change the import paths as much and it also
gets rid of the need for export_test.go to bridge.
Also, correct a couple of comments while here.
The dcrwallet command to set multiple tickets vote bits fields at
the same time has been added. Functions to encode/decode relevant
hex strings (as passed over JSON) were also added, along with tests.
