Clean up editorclass externs into one location

Again, like the previous commit, it should just be put in the header
file of its respective class instead of being a mess everywhere.

desktop_version/src/Map.cpp

@@ -2,10 +2,6 @@
 
 #include "MakeAndPlay.h"
 
-#if !defined(NO_CUSTOM_LEVELS)
-extern editorclass ed;
-#endif
-
 mapclass::mapclass()
 {
 	//Start here!

desktop_version/src/Map.h

@@ -13,10 +13,6 @@
 #include "Music.h"
 #include "editor.h"
 
-#if !defined(NO_CUSTOM_LEVELS)
-extern editorclass ed;
-#endif
-
 class mapclass
 {
 public:

desktop_version/src/editor.cpp

@@ -2070,8 +2070,6 @@ void fillboxabs( int x, int y, int x2, int y2, int c )
 }
 
 
-extern editorclass ed;
-
 void editorclass::generatecustomminimap()
 {
     map.customwidth=mapwidth;

desktop_version/src/editor.h

@@ -248,6 +248,8 @@ void editorlogic();
 
 void editorinput();
 
+extern editorclass ed;
+
 #endif /* EDITOR_H */
 
 #endif /* NO_CUSTOM_LEVELS */