Include nothing before Audacity.h, as comments say we should...

... and remove some duplicated inclusions

src/prefs/ExtImportPrefs.cpp

@@ -21,7 +21,6 @@
 #include <wx/listctrl.h>
 #include <wx/dnd.h>
 
-#include "../Audacity.h"
 #include "../Prefs.h"
 #include "../ShuttleGui.h"
 #include "../widgets/ErrorDialog.h"

src/prefs/KeyConfigPrefs.cpp

@@ -20,6 +20,7 @@ KeyConfigPrefs and MousePrefs use.
 *//*********************************************************************/
 
 #include "../Audacity.h"
+
 #include "../Experimental.h"
 #include "KeyConfigPrefs.h"
 

src/prefs/MidiIOPrefs.cpp

@@ -24,6 +24,7 @@ other settings.
 *//********************************************************************/
 
 #include "../Audacity.h"
+
 #include "../Experimental.h"
 #ifdef EXPERIMENTAL_MIDI_OUT
 

src/prefs/MousePrefs.cpp

@@ -33,6 +33,7 @@
 *//********************************************************************/
 
 #include "../Audacity.h"
+
 #include "../Experimental.h"
 #include "MousePrefs.h"
 

src/prefs/RecordingPrefs.cpp

@@ -19,6 +19,7 @@
 *//********************************************************************/
 
 #include "../Audacity.h"
+
 #include "../Experimental.h"
 #include "RecordingPrefs.h"
 

src/prefs/SpectrogramSettings.cpp

@@ -15,6 +15,7 @@ Paul Licameli
 
 #include "../Audacity.h"
 #include "SpectrogramSettings.h"
+
 #include "../NumberScale.h"
 #include "../TranslatableStringArray.h"
 

src/prefs/WaveformPrefs.cpp

@@ -15,6 +15,7 @@ Paul Licameli
 
 #include "../Audacity.h"
 #include "WaveformPrefs.h"
+
 #include "GUIPrefs.h"
 #include "GUISettings.h"
 

src/prefs/WaveformSettings.cpp

@@ -15,6 +15,7 @@ Paul Licameli
 
 #include "../Audacity.h"
 #include "WaveformSettings.h"
+
 #include "GUISettings.h"
 #include "GUIPrefs.h"