QtcProcess: Remove TerminalMode::Pty enum value

Make Pty::Data optional. When set, the PtyProcessImpl
implementation is implied.

Change-Id: I7990e9d9016223e6597d876a5d0c4ed177365874
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/docker/dockerdevice.cpp

@@ -304,7 +304,7 @@ void DockerProcessImpl::start()
                                              m_setup.m_workingDirectory,
                                              interactive,
                                              true,
-                                             m_setup.m_terminalMode == TerminalMode::Pty);
+                                             m_setup.m_ptyData.has_value());
 
     m_process.setCommand(fullCommandLine);
     m_process.start();