all: remove dependency on proto v1

This does not remove all dependencies,
but all of the cases where it can now be implemented in terms of v2.

Change-Id: Idc5b0273f0d35c284bf2141eb9cce998692ceb15
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/184878
Reviewed-by: Herbie Ong <herbie@google.com>
diff --git a/internal/filedesc/build_test.go b/internal/filedesc/build_test.go
index edeb56e..3a4f5ae 100644
--- a/internal/filedesc/build_test.go
+++ b/internal/filedesc/build_test.go
@@ -10,7 +10,7 @@
 	"io/ioutil"
 	"testing"
 
-	proto "github.com/golang/protobuf/proto"
+	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/reflect/protodesc"
 	"google.golang.org/protobuf/reflect/protoreflect"