[btcsuite/btcutil] e33083: Remove error return from Block.Sha function.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcutil
  Commit: e33083890094ed26340ef8223b9f13dfd2b2a8a3
      
https://github.com/btcsuite/btcutil/commit/e33083890094ed26340ef8223b9f13dfd2b2a8a3
  Author: Dave Collins <da...@conformal.com>
  Date:   2015-04-17 (Fri, 17 Apr 2015)

  Changed paths:
    M block.go
    M block_test.go

  Log Message:
  -----------
  Remove error return from Block.Sha function.

This commit remove the error return from the Block.Sha function since it
can never fail and ends up causing a lot of unneeded error checking
throughout the code base.