build: enable goimports and varcheck linters (#16446)

core/asm/compiler.go

@@ -17,7 +17,6 @@
 package asm
 
 import (
-	"errors"
 	"fmt"
 	"math/big"
 	"os"
@@ -264,11 +263,6 @@ func (err compileError) Error() string {
 	return fmt.Sprintf("%d syntax error: unexpected %v, expected %v", err.lineno, err.got, err.want)
 }
 
-var (
-	errExpBol            = errors.New("expected beginning of line")
-	errExpElementOrLabel = errors.New("expected beginning of line")
-)
-
 func compileErr(c token, got, want string) error {
 	return compileError{
 		got:    got,

core/tx_pool.go

@@ -38,8 +38,6 @@ import (
 const (
 	// chainHeadChanSize is the size of channel listening to ChainHeadEvent.
 	chainHeadChanSize = 10
-	// rmTxChanSize is the size of channel listening to RemovedTransactionEvent.
-	rmTxChanSize = 10
 )
 
 var (

core/types/transaction.go

@@ -33,7 +33,6 @@ import (
 
 var (
 	ErrInvalidSig = errors.New("invalid transaction v, r, s values")
-	errNoSigner   = errors.New("missing signing methods")
 )
 
 // deriveSigner makes a *best* guess about which signer to use.

core/vm/instructions.go

@@ -31,7 +31,6 @@ import (
 var (
 	bigZero                  = new(big.Int)
 	tt255                    = math.BigPow(2, 255)
-	tt256                    = math.BigPow(2, 256)
 	errWriteProtection       = errors.New("evm: write protection")
 	errReturnDataOutOfBounds = errors.New("evm: return data out of bounds")
 	errExecutionReverted     = errors.New("evm: execution reverted")