Update xmllite reference to new source location

In https://codereview.chromium.org/2443903004/ all of
third_party/webrtc/libjingle was replaced with a new imported
copy in third_party/libjingle_xmpp.
Unfortunately https://codereview.chromium.org/2586403003
was submitted in the meantime, before the code was deleted
in the WebRTC repo and rolled into Chromium.

This CL updates the last references to the old copy of the code,
which should enable deleting it from WebRTC.

BUG=webrtc:5539
[email protected]

Review-Url: https://codereview.chromium.org/2616873002
Cr-Commit-Position: refs/heads/master@{#441609}
1 file changed