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/proto/equal.go b/proto/equal.go
index 3931b1a..a5a0acb 100644
--- a/proto/equal.go
+++ b/proto/equal.go
@@ -7,7 +7,7 @@
 import (
 	"bytes"
 
-	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
 )
 
 // Equal returns true of two messages are equal.