Get rid of TestNetscapePlugIn/ dir from DumpRenderTree.

Aparently the remaining files in there are unused and thus can be removed.

BUG=None
R=abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/21968003

git-svn-id: svn://svn.chromium.org/blink/trunk@155575 bbb929c8-8fbe-4397-9dbb-9b2b20218538