Utils: Re-do Replace SynchronousCommand::flags by a named bool

The potential extensibility was never used, and a similar use case
in QtcProcess (setLowPriority()) used a named setter.

Change-Id: I87d84ea2206995d5069265f8df78f40cf2ba8a36
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/libs/utils/shellcommand.h

@@ -141,6 +141,7 @@ public:
     void setProgressiveOutput(bool progressive);
 
     void setOutputProxyFactory(const std::function<OutputProxy *()> &factory);
+    void setDisableUnixTerminal();
 
     // This is called once per job in a thread.
     // When called from the UI thread it will execute fully synchronously, so no signals will
@@ -162,7 +163,6 @@ signals:
     void terminate(); // Internal
 
 protected:
-    virtual unsigned processFlags() const;
     virtual void addTask(QFuture<void> &future);
     int timeoutS() const;
     QString workDirectory(const QString &wd) const;