go.mod: temporarily delete go.mod file

Change-Id: I538adc19970b1a3a88d3b1558bd7f858de0129a7
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/166886
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

go.mod

@@ -1,3 +0,0 @@
-module github.com/golang/protobuf
-
-require github.com/golang/protobuf/v2 v2.0.0-20190311214845-9d8c804b555c