Remove blind work

If the problem is that bitcoind falls behind, let's catch it up then!

Remove "Blind Work" and SUBSIDY_FUNC yielding the following advantages:

* Doesn't depend on SUBSIDY_FUNC
* Doesn't work on fee-less blocks as long as there are fees to be had
* More money for miners
* Keeps the coin network more up-to-date and healthy
* Keeps the blockchain clean of transactionless blocks as long as there are transactions to be mined
* Resolves https://github.com/Rav3nPL/p2pool-rav/issues/33

Disadvantages:

* Incompatible with old-buggy-bitcoind based coins
* Will have slightly more DOAs until a substantial portion of the network updates

Been testing this for weeks, works great!

Paging @forrestv to this pull request.