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/internal/encoding/defval/default_test.go b/internal/encoding/defval/default_test.go
index e91eb7e..a25a93f 100644
--- a/internal/encoding/defval/default_test.go
+++ b/internal/encoding/defval/default_test.go
@@ -9,7 +9,7 @@
 	"reflect"
 	"testing"
 
-	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
 
 func Test(t *testing.T) {