This reverts commit 79759fea, reversing
changes made to dc36f4df.

This reverts commit 5e01e2ac.

Change names to StreamedUnary, ServerUnaryStreamer, etc. Use a templated method handler since most code shared between the new StreamedUnary and the existing BidiStreaming. Eliminate the separate enum case for streamed unary. Return a status failure if a StreamedUnary method handler doesn't actually do a write (since that is
violating the appearance of unary-ness)

ServerReaderWriterInterface so that some functions can be made
to accept either.

C++ Compression Level set properly

There is a comment above IsCancelled that says when it is ok to use this.