Replace golang.org/x/net/context with std library

Signed-off-by: Shengjing Zhu <zhsj@debian.org>

pkg/cri/server/image_pull.go

@@ -17,6 +17,7 @@
 package server
 
 import (
+	"context"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/base64"
@@ -40,7 +41,6 @@ import (
 	"github.com/containerd/imgcrypt"
 	"github.com/containerd/imgcrypt/images/encryption"
 	imagespec "github.com/opencontainers/image-spec/specs-go/v1"
-	"golang.org/x/net/context"
 	runtime "k8s.io/cri-api/pkg/apis/runtime/v1"
 
 	criconfig "github.com/containerd/containerd/pkg/cri/config"