code-highlight-gadget.xml: remove wave-api external script

"wave.js" is 404 Not Found on wave-api.appspot.com. Looks like gadget works without this file, "wave.js" feature already included in server output.
Merge pull request #4 from nilya/patch-1

code-highlight-gadget.xml: remove wave-api external script
If ilya says it works it must work! :)