all: change module to google.golang.org/protobuf

Temporarily remove go.mod, since we can't generate an accurate one until
the corresponding v1 change is submitted.

Change-Id: I1e1ad97f2b455e33f61ffaeb8676289795e47e72
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/177000
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/testing/prototest/prototest.go b/testing/prototest/prototest.go
index 058ef24..c9f7c7a 100644
--- a/testing/prototest/prototest.go
+++ b/testing/prototest/prototest.go
@@ -12,9 +12,9 @@
 	"sort"
 	"testing"
 
-	textpb "github.com/golang/protobuf/v2/encoding/textpb"
-	"github.com/golang/protobuf/v2/proto"
-	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
+	textpb "google.golang.org/protobuf/encoding/textpb"
+	"google.golang.org/protobuf/proto"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
 
 // TestMessage runs the provided message through a series of tests