all: swap out the C++ ethash to the pure Go one (mining todo)

accounts/abi/bind/backends/simulated.go

cmd/utils/flags.go

core/bench_test.go

core/block_validator.go

core/block_validator_test.go

core/blockchain.go

core/blockchain_test.go

core/chain_makers.go

core/chain_makers_test.go

core/chain_pow.go

core/chain_pow_test.go

core/dao_test.go

eth/backend.go

eth/handler_test.go

eth/helper_test.go

internal/ethapi/api.go

les/helper_test.go

light/lightchain.go

light/lightchain_test.go

light/odr_test.go