Remove libtrust from handler tests

It was used for signing schema v1 manifests in tests which have now been
removed so there is no point in keeping these there anymore.

Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>

registry/handlers/api_test.go

@@ -31,7 +31,6 @@ import (
 	_ "github.com/distribution/distribution/v3/registry/storage/driver/inmemory"
 	"github.com/distribution/distribution/v3/testutil"
 	"github.com/distribution/reference"
-	"github.com/docker/libtrust"
 	"github.com/gorilla/handlers"
 	"github.com/opencontainers/go-digest"
 )
@@ -2128,7 +2127,6 @@ func testManifestDelete(t *testing.T, env *testEnv, args manifestArgs) {
 }
 
 type testEnv struct {
-	pk      libtrust.PrivateKey
 	ctx     context.Context
 	config  configuration.Configuration
 	app     *App
@@ -2186,13 +2184,7 @@ func newTestEnvWithConfig(t *testing.T, config *configuration.Configuration) *te
 		t.Fatalf("error creating url builder: %v", err)
 	}
 
-	pk, err := libtrust.GenerateECP256PrivateKey()
-	if err != nil {
-		t.Fatalf("unexpected error generating private key: %v", err)
-	}
-
 	return &testEnv{
-		pk:      pk,
 		ctx:     ctx,
 		config:  *config,
 		app:     app,