Remove unnecessary "script src=..." from MediaTest.gwt.xml to avoid virus scanner false positives

A user reported that Sophos antivirus was flagging MediaTest.gwt.xml (see: http://savmac7-20.p.link.sophos.com/t/en/Mal/Badsrc-D). The script src=... line isn't necessary anyway, so I'm removing those lines.

Review at http://gwt-code-reviews.appspot.com/1341801

Review by: rice@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9671 8db76d5a-ed1c-0410-87a9-c151d255dfc7