Fix jshint failure in horizon.d3piechart.js

The var "item" on line 240 was explicitly being set to "undefined",
which is unnecessary.

Change-Id: Ia4cb8f868a4b201e578157a8ad5c5e552ab6ac8a
Closes-bug: 1378766
Merge "Fix jshint failure in horizon.d3piechart.js"