hotkey: Use $.each instead of 'in'

This is simpler and more consistent with the rest of our code.

(imported from commit 5188b8047952fe4e6556a26f10ab93123d67e03f)

zephyr/static/js/hotkey.js

@@ -6,10 +6,9 @@ var pressed_keys = {};
 
 function num_pressed_keys() {
     var size = 0, key;
-    for (key in pressed_keys) {
-        if (pressed_keys.hasOwnProperty(key))
-            size++;
-    }
+    $.each(pressed_keys, function () {
+        size++;
+    });
     return size;
 }