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_test.go b/testing/prototest/prototest_test.go
index 5e4902f..82eb5b2 100644
--- a/testing/prototest/prototest_test.go
+++ b/testing/prototest/prototest_test.go
@@ -8,10 +8,10 @@
 	"fmt"
 	"testing"
 
-	testpb "github.com/golang/protobuf/v2/internal/testprotos/test"
-	test3pb "github.com/golang/protobuf/v2/internal/testprotos/test3"
-	"github.com/golang/protobuf/v2/proto"
-	"github.com/golang/protobuf/v2/testing/prototest"
+	testpb "google.golang.org/protobuf/internal/testprotos/test"
+	test3pb "google.golang.org/protobuf/internal/testprotos/test3"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/testing/prototest"
 )
 
 func Test(t *testing.T) {