Remove ACT_KEYMAP and ACT_OVERLAY

- Remove ACT_OVERLAY
- Rename ACT_KEYMAP to ACT_LAYER
- Add ACT_LAYER_BITOP

common/command.c

@@ -575,6 +575,5 @@ static void switch_default_layer(uint8_t layer)
 {
     print("switch_default_layer: "); print_dec(default_layer); print(" to "); print_dec(layer); print("\n");
     default_layer_set(layer);
-    overlay_clear();
     clear_keyboard();
 }