[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_stream/session.h

@@ -36,8 +36,6 @@ class Process;
 struct SessionTarget {
   // SSH username and hostname of the remote target, formed as [user@]host.
   std::string user_host;
-  // Port to use for SSH connections to the remote target.
-  uint16_t ssh_port;
   // Ssh command to use to connect to the remote target.
   std::string ssh_command;
   // Scp command to use to copy files to the remote target.