Terminal: Use QtcProcess to start terminal window

Previously DesktopDevice::openTerminal used custom code to open a
terminal window. This patch changes it to use QtcProcess with
TerminalMode::On.

This also removes the need for "openTerminal.py" on macOS.

Change-Id: Iec978bdd19487ff8e59dcd88c35c2d01b0681022
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/libs/utils/launchersocket.cpp

@@ -257,6 +257,7 @@ void CallerHandle::start(const QString &program, const QStringList &arguments)
     p.unixTerminalDisabled = m_setup->m_unixTerminalDisabled;
     p.useCtrlCStub = m_setup->m_useCtrlCStub;
     p.reaperTimeout = m_setup->m_reaperTimeout;
+    p.createConsoleOnWindows = m_setup->m_createConsoleOnWindows;
     sendPacket(p);
 }