We are currently using the `base58::Error` type to create errors in
`bitcoin`, these are bitcoin errors not `base58` errors.
Note that we add what looks like duplicate
`InvalidBase58PayloadLengthError` types but they are different because
of the expected length. This could have been a field but I elected not
to do so for two reasons:
1. We will need to do so anyways if we crate smash more
2. The `crypto::key` one can have one of two values 33 or 34.
With this applied we can remove the now unused error variants from
`base58::Error`.
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