contrib: remove getwork-based pyminer

As the `getwork` API doesn't exist anymore, currently this script is useless.

It would be nice to have a `getblocktemplate`-based Python example of a
miner, but there is no point in keeping this one around except to
confuse people.
Merge branch '2014_07_remove_pyminer' of git://github.com/laanwj/bitcoin into merge-pyminer