context: remove definition of Context

Back in the before time, the best practices surrounding usage of Context
weren't quite worked out. We defined our own type to make usage easier.
As this packaged was used elsewhere, it make it more and more
challenging to integrate with the forked `Context` type. Now that it is
available in the standard library, we can just use that one directly.

To make usage more consistent, we now use `dcontext` when referring to
the distribution context package.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

registry/auth/silly/access.go

@@ -8,11 +8,12 @@
 package silly
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"strings"
 
-	"github.com/docker/distribution/context"
+	dcontext "github.com/docker/distribution/context"
 	"github.com/docker/distribution/registry/auth"
 )
 
@@ -43,7 +44,7 @@ func newAccessController(options map[string]interface{}) (auth.AccessController,
 // Authorized simply checks for the existence of the authorization header,
 // responding with a bearer challenge if it doesn't exist.
 func (ac *accessController) Authorized(ctx context.Context, accessRecords ...auth.Access) (context.Context, error) {
-	req, err := context.GetRequest(ctx)
+	req, err := dcontext.GetRequest(ctx)
 	if err != nil {
 		return nil, err
 	}
@@ -65,7 +66,11 @@ func (ac *accessController) Authorized(ctx context.Context, accessRecords ...aut
 		return nil, &challenge
 	}
 
-	return auth.WithUser(ctx, auth.UserInfo{Name: "silly"}), nil
+	ctx = auth.WithUser(ctx, auth.UserInfo{Name: "silly"})
+	ctx = dcontext.WithLogger(ctx, dcontext.GetLogger(ctx, auth.UserNameKey, auth.UserKey))
+
+	return ctx, nil
+
 }
 
 type challenge struct {