Remove NO_EDITOR/NO_CUSTOM_LEVELS, disable editor on Steam Deck

This commit removes the `NO_EDITOR` and `NO_CUSTOM_LEVELS` defines,
which cleans up the code a lot, and they weren't really needed anyways.

This commit also disables the editor on the Steam Deck, and adds a
program argument to re-enable the editor, `-enable-editor`.

desktop_version/src/Font.cpp

@@ -548,9 +548,7 @@ void set_level_font_new(void)
         }
     }
 
-#ifndef NO_CUSTOM_LEVELS
     cl.level_font_name = get_main_font_name(font_idx_level);
-#endif
 }
 
 static void fill_map_name_idx(FontContainer* container)