Review use of go-spew in production code

[jholdstock]

davecgh/go-spew is used in production code:

dcrpool/pool/client.go

Line 695 in f818a93

log.Errorf("unexpected response message: %v", spew.Sdump(resp))

I believe we should be avoiding the use of go-spew in production code as it has a dependency on the unsafe package.

A comment from jrick on the topic: davecgh/go-spew#106

We also use it a few times in the CPU miner, but I guess this is acceptable as the CPU miner is only intended for testing.

fyi: @davecgh, @jrick

[dnldd]

I'm opting to remove the use of spew entirely, relegating to using it only when debugging locally. I noticed most of the cases where spew was being used were related to debugging scenarios where more information was needed, this isn't needed in production code. In other cases spew was being used to output more information than necessary, particularly in tests.

[davecgh]

This is fine for dcrpool, but I can say that spew will not be removed from use in dcrd because it is used for trace logging which is extremely useful when dealing with protocol level things.