removed dead link to ProtoSharp (#5610)
removed dead link to ProtoSharp (#5610)

I tried finding an active repo on github with no success.  The only ProtoSharp I found wasn't related to PB at all.
google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf