go.mod: temporarily delete go.mod file
go.mod: temporarily delete go.mod file

Change-Id: I23933890226513318f13094009167aa7922361b4
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/166885
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>

protocolbuffers/protobuf-go,protocolbuffers/protobuf-go