crypto/tls: use new ecdsa.VerifyASN1 API

Change-Id: I2a233190bda78ca022ff4074b4553788847d7583
Reviewed-on: https://go-review.googlesource.com/c/go/+/220720
Run-TryBot: Katie Hockman <katie@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>

common.go

@@ -19,7 +19,6 @@ import (
 	"fmt"
 	"internal/cpu"
 	"io"
-	"math/big"
 	"net"
 	"strings"
 	"sync"
@@ -1264,13 +1263,6 @@ func (c *lruSessionCache) Get(sessionKey string) (*ClientSessionState, bool) {
 	return nil, false
 }
 
-// TODO(jsing): Make these available to both crypto/x509 and crypto/tls.
-type dsaSignature struct {
-	R, S *big.Int
-}
-
-type ecdsaSignature dsaSignature
-
 var emptyConfig Config
 
 func defaultConfig() *Config {