Remove unnecessary middleman ed.swapmap

When the game loads a room in a custom level, previously it would load
the tilemap of that room into ed.swapmap, and then mapclass::loadlevel()
would manually go through each element in ed.swapmap to set each tile in
`contents`. Why do that, when you can just return the vector from
editorclass::loadlevel() and set it directly? ed.swapmap is really
unnecessary.

desktop_version/src/editor.h

@@ -95,7 +95,7 @@ class editorclass{
 
   void saveconvertor();
   void reset();
-  void loadlevel(int rxi, int ryi);
+  std::vector<int> loadlevel(int rxi, int ryi);
 
   void placetile(int x, int y, int t);
 
@@ -147,7 +147,6 @@ class editorclass{
   int getwarpbackground(int rx, int ry);
 
   std::vector<std::string> getLevelDirFileNames( );
-  std::vector <int> swapmap;
   std::vector <int> contents;
   std::vector <int> vmult;
   int numtrinkets();