all: remove ethash pow, only retain shims needed for consensus and tests (#27178)

* all: remove ethash pow, only retain shims needed for consensus and tests

* all: thank you linter

* all: disallow launching Geth in legacy PoW mode

* cmd/env/internal/t8ntool: remove dangling ethash flag

console/console_test.go

@@ -26,7 +26,6 @@ import (
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/consensus/ethash"
 	"github.com/ethereum/go-ethereum/console/prompt"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/eth"
@@ -99,9 +98,6 @@ func newTester(t *testing.T, confOverride func(*ethconfig.Config)) *tester {
 		Miner: miner.Config{
 			Etherbase: common.HexToAddress(testAddress),
 		},
-		Ethash: ethash.Config{
-			PowMode: ethash.ModeTest,
-		},
 	}
 	if confOverride != nil {
 		confOverride(ethConf)