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/proto_methods.go b/proto/proto_methods.go
index 360a1ee..61349f4 100644
--- a/proto/proto_methods.go
+++ b/proto/proto_methods.go
@@ -7,7 +7,7 @@
 
 package proto
 
-import "github.com/golang/protobuf/v2/runtime/protoiface"
+import "google.golang.org/protobuf/runtime/protoiface"
 
 func protoMethods(m Message) *protoiface.Methods {
 	if x, ok := m.(protoiface.Methoder); ok {