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/proto/equal_test.go b/proto/equal_test.go
index 99f1720..568312f 100644
--- a/proto/equal_test.go
+++ b/proto/equal_test.go
@@ -393,16 +393,16 @@
 	// Extensions.
 	{
 		build(&testpb.TestAllExtensions{},
-			extend(testpb.E_OptionalInt32Extension, scalar.Int32(1)),
+			extend(testpb.E_OptionalInt32Extension, int32(1)),
 		),
 		build(&testpb.TestAllExtensions{},
-			extend(testpb.E_OptionalInt32Extension, scalar.Int32(2)),
+			extend(testpb.E_OptionalInt32Extension, int32(2)),
 		),
 	},
 	{
 		&testpb.TestAllExtensions{},
 		build(&testpb.TestAllExtensions{},
-			extend(testpb.E_OptionalInt32Extension, scalar.Int32(2)),
+			extend(testpb.E_OptionalInt32Extension, int32(2)),
 		),
 	},
 	// Proto2 default values are not considered by Equal, so the following are still unequal.