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/json/string.go b/internal/encoding/json/string.go
index 7f70cff..1d89aca 100644
--- a/internal/encoding/json/string.go
+++ b/internal/encoding/json/string.go
@@ -12,7 +12,7 @@
 	"unicode/utf16"
 	"unicode/utf8"
 
-	"github.com/golang/protobuf/v2/internal/errors"
+	"google.golang.org/protobuf/internal/errors"
 )
 
 func appendString(out []byte, in string) ([]byte, error) {