Remove deprecated parameter in Casper unread test

You used to have to call casper.test.done(N) where N was the number of
tests run. This is no longer required and is deprecated in CasperJS 1.1.

(imported from commit 0de9ecb1930cbce416fa02c24a882e926cdc8e87)

zerver/tests/frontend/tests/06-unread.js

@@ -101,5 +101,5 @@ casper.then(function () {
 
 // Run the above queued actions.
 casper.run(function () {
-    casper.test.done(3);
+    casper.test.done();
 });