Remove ErrorDialog.h from .h files (one function moves out of line)

src/commands/CommandTargets.cpp

@@ -27,6 +27,7 @@ capture the more lengthy output from some commands.
 #include <wx/string.h>
 #include "../ShuttleGui.h"
 #include "../Project.h"
+#include "../widgets/ErrorDialog.h"
 
 void CommandMessageTarget::StartArray()
 {
@@ -237,6 +238,12 @@ void BriefCommandMessageTarget::EndField(){
 }
 
 
+void MessageBoxTarget::Update(const wxString &message)
+{
+   AudacityMessageBox(message);
+}
+
+
 LispifiedCommandOutputTargets::LispifiedCommandOutputTargets( CommandOutputTargets & target )
  : CommandOutputTargets() ,
    pToRestore( &target )

src/commands/CommandTargets.h

@@ -60,7 +60,6 @@ and sends it to that message target.
 //#include "../src/Project.h"
 #include "../widgets/ProgressDialog.h"
 #include "../commands/ResponseQueue.h"
-#include "../widgets/ErrorDialog.h"
 
 class wxStatusBar;
 
@@ -204,10 +203,7 @@ class MessageBoxTarget final : public CommandMessageTarget
 {
 public:
    virtual ~MessageBoxTarget() {}
-   void Update(const wxString &message) override
-   {
-      AudacityMessageBox(message);
-   }
+   void Update(const wxString &message) override;
 };
 
 /// Displays messages from a command in a wxStatusBar