minor cleanup

sim/libmbit.ts

@@ -3,16 +3,12 @@
 
 namespace ks.rt.micro_bit {
     export function initCurrentRuntime() {
-        initBoard();
-    }
-
-    ks.rt.initCurrentRuntime = initCurrentRuntime;
-
-    function initBoard() {
         U.assert(!runtime.board)
         runtime.board = new Board()
     }
 
+    ks.rt.initCurrentRuntime = initCurrentRuntime;
+
     export function board() {
         return runtime.board as Board
     }