Remove (or comment) ProgressDialog.h in headers...

... For ImportPlugin, use unique_ptr not Maybe to hold it, and take constructors
out-of-line.

src/commands/AudacityCommand.h

@@ -24,7 +24,6 @@ class wxWindow;
 #include "../SampleFormat.h"
 #include "../SelectedRegion.h"
 #include "../Internat.h"
-#include "../widgets/ProgressDialog.h"
 #include "../include/audacity/ComponentInterface.h"
 #include "../include/audacity/EffectAutomationParameters.h" // for command automation
 

src/commands/CommandTargets.h

@@ -58,7 +58,6 @@ and sends it to that message target.
 #include "../MemoryX.h"
 #include <vector>
 //#include "../src/Project.h"
-#include "../widgets/ProgressDialog.h"
 #include "../commands/ResponseQueue.h"
 
 class wxStatusBar;
@@ -155,6 +154,10 @@ public:
    void Update(double WXUNUSED(completed)) override {}
 };
 
+#if 0
+
+#include "../widgets/ProgressDialog.h" // Member variable
+
 /// Sends command progress information to a ProgressDialog
 class GUIProgressTarget final : public CommandProgressTarget
 {
@@ -170,6 +173,7 @@ public:
       mProgress.Update(completed);
    }
 };
+#endif
 
 
 ///