change isDeleting to isUnsetting

- DocumentObject::isDeleting was changed to isRemoving.
  This commit just prevents future confusion.

src/Mod/TechDraw/App/DrawViewCollection.h

@@ -49,7 +49,7 @@ public:
     int addView(DrawView *view);
     int removeView(DrawView *view);
     void rebuildViewList(void);
-    bool isDeleting(void) { return nowDeleting; }
+    bool isUnsetting(void) { return nowUnsetting; }
 
     int countChildren();
 
@@ -65,7 +65,7 @@ public:
 
 protected:
     void onChanged(const App::Property* prop);
-    bool nowDeleting;
+    bool nowUnsetting;
 };
 
 } //namespace TechDraw