clean up some internal path and names

interop/empty.proto

@@ -40,10 +40,4 @@ package grpc.testing;
 //     rpc Bar (grpc.testing.Empty) returns (grpc.testing.Empty) { };
 //   };
 //
-// MOE:begin_strip
-// The difference between this one and net/rpc/empty-message.proto is that
-// 1) The generated message here is in proto2 C++ API.
-// 2) The proto2.Empty has minimum dependencies
-//    (no message_set or net/rpc dependencies)
-// MOE:end_strip
 message Empty {}