converted spawn into a overlay-based rendermode

src/rendermodes.c

@@ -31,10 +31,6 @@ RenderModeInterface *get_render_mode(RenderState *state) {
         iface = &rendermode_night;
     } else if (strcmp(rendermode, "spawn") == 0) {
         iface = &rendermode_spawn;
-    } else if (strcmp(rendermode, "overlay") == 0) {
-        /* TODO temporarily use overlay directly, but later on
-           you want to use overlay-derived modes */
-        iface = &rendermode_overlay;
     }
     
     Py_DECREF(rendermode_py);