[cdc_rsync] [cdc_stream] Remove SSH port argument (#41)

This CL removes the port arguments for both tools.

The port argument can also be specified via the ssh-command and
scp-command flags. In fact, if a port is specified by both port flags
and ssh/scp commands, they interfere with each other. For ssh, the one
specified in ssh-command wins. For scp, the one specified in
scp-command wins. To fix this, one would have to parse scp-command and
remove the port arg there. Or we could just remove the ssh-port arg.
This is what this CL does. Note that if you need a custom port, it's
very likely that you also have to define custom ssh and scp commands.

cdc_rsync/cdc_rsync_client.h

@@ -36,7 +36,6 @@ class ZstdStream;
 class CdcRsyncClient {
  public:
   struct Options {
-    int port = RemoteUtil::kDefaultSshPort;
     bool delete_ = false;
     bool recursive = false;
     int verbosity = 0;
@@ -118,7 +117,6 @@ class CdcRsyncClient {
 
   Options options_;
   std::vector<std::string> sources_;
-  const std::string user_host_;
   const std::string destination_;
   WinProcessFactory process_factory_;
   RemoteUtil remote_util_;