core: move error variable to error.go (#19560)

* move error variable to error.go

* Update error.go

Edit "Genesis" to "genesis"

core/blockchain.go

@@ -63,8 +63,6 @@ var (
 
 	blockPrefetchExecuteTimer   = metrics.NewRegisteredTimer("chain/prefetch/executes", nil)
 	blockPrefetchInterruptMeter = metrics.NewRegisteredMeter("chain/prefetch/interrupts", nil)	
-
-	ErrNoGenesis = errors.New("Genesis not found in chain")
 )
 
 const (

core/error.go

@@ -32,4 +32,7 @@ var (
 	// ErrNonceTooHigh is returned if the nonce of a transaction is higher than the
 	// next one expected based on the local chain.
 	ErrNonceTooHigh = errors.New("nonce too high")
+
+	// ErrNoGenesis is returned when there is no Genesis Block.
+	ErrNoGenesis = errors.New("genesis not found in chain")
 )