In this commit, we update to the latest version of btcutil which
contains a bug fix for filter matching, and as optimizations speed up
both filter matching and constructions.
In this commit, we update to the latest version of `btcutil`. This version
contains a bug fix for the neutrino filter generation. The implementation
within `btcutil` didn't fully comply with the BIP specification as it
included some OP_RETURN outputs, rather than excluding them all. As a
result, any active `btcd` node on mainnet/testnet will need to _drop their
entire `cfindex`_ and re-index after this is merged in.
