Remove btcd/wire dependency.

[jrick]

Fixes #228.

[davecgh]

I like the concept. The only part I question is that I believe btcd/wire uses the fastsha256 package and I think that package is also used elsewhere within Decred, so I think this will end up resulting in having duplicate sha code. That said, I don't believe there is really any reason for Decred to continue using that package as the only reason it still exists is because the getwork RPC in btcd requires access to the midstate whereas I'm fairly certain Decred does not include it.

OK.

[jrick]

right, we don't need fastsha256 for decred anymore, anywhere.

[alexlyp]

OK

[jcvernaleo]

I'm always happy for one less dependence. OK from me too (but if you want to wait until after the sync this one can sit until then). Doesn't matter to me.

[cjepson]

OK