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/legacy/message.go b/internal/legacy/message.go
index ee242ca..174615d 100644
--- a/internal/legacy/message.go
+++ b/internal/legacy/message.go
@@ -11,10 +11,10 @@
 	"sync"
 	"unicode"
 
-	ptag "github.com/golang/protobuf/v2/internal/encoding/tag"
-	pimpl "github.com/golang/protobuf/v2/internal/impl"
-	ptype "github.com/golang/protobuf/v2/internal/prototype"
-	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
+	ptag "google.golang.org/protobuf/internal/encoding/tag"
+	pimpl "google.golang.org/protobuf/internal/impl"
+	ptype "google.golang.org/protobuf/internal/prototype"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
 
 // wrapMessage wraps v as a protoreflect.ProtoMessage,