JSON tests fail, as we're not using OriginalNameAttribute yet.

Everything should now be consistent - the only difference between files is the year (aside from generated files).

Fixes issue #531.

- Remove some old proto2-based C#-only messages
- Remove the "build" directory which only contained out-of-date files
- Remove the csharp_namespace option from proto2 messages
- Change "Google.ProtocolBuffers" to "Google.Protobuf" in other messages