Removed conflicting C# version line
Removed conflicting C# version line

Somehow we ended up with two conflicting versions listed for C#, so this
commit removes the incorrect one (the correct one is 3.13.0-rc3).

google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf