Don't use wxArrayPtrVoid with casts, use std::vector

src/export/ExportMultiple.h

@@ -29,6 +29,7 @@ class wxTextCtrl;
 class AudacityProject;
 class LabelTrack;
 class ShuttleGui;
+class Track;
 
 class ExportMultiple final : public wxDialogWrapper
 {
@@ -111,7 +112,10 @@ private:
    LabelTrack *mLabels;
    int mNumLabels;
    int mNumWaveTracks;
-   wxArrayPtrVoid mSelected;
+
+   // PRL:  This is never populated anywhere?
+   std::vector<Track*> mSelected;
+
    int mFilterIndex;          /**< The index in the drop-down list of export
                                 formats (mFormat) of the selected export format.
                                 This list includes all possible