Update boot.js

Co-authored-by: Rob Pilling <robpilling@gmail.com>

Author: RKBoss6

apps/backlite/boot.js

@@ -13,7 +13,7 @@
   s.brightness = 0;
   require("Storage").writeJSON("setting.json", s);
   //remove large settings object from memory
-  s=null;
+  delete s;
   const longPressTime=400; //(ms)
 
   Bangle.on('lock', function(isLocked) {