configs/configupgrade: Use mock provider instead of test provider

The test provider comes with a lot of baggage since it's designed to be
used as a plugin, so instead we'll just use the mock provider
implementation directly, and so we can (in a later commit) configure it
appropriately for what our tests need here.

configs/configupgrade/upgrade_test.go

@@ -9,8 +9,8 @@ import (
 	"path/filepath"
 	"testing"
 
-	testprovider "github.com/hashicorp/terraform/builtin/providers/test"
 	"github.com/hashicorp/terraform/providers"
+	"github.com/hashicorp/terraform/terraform"
 )
 
 func TestUpgradeValid(t *testing.T) {
@@ -178,6 +178,7 @@ func diffSourceFilesFallback(got, want []byte) []byte {
 
 var testProviders = map[string]providers.Factory{
 	"test": providers.Factory(func() (providers.Interface, error) {
-		return testprovider.Provider(), nil
+		p := &terraform.MockProvider{}
+		return p, nil
 	}),
 }