Don't hide the New Message button when you click on it.

It's not part of the original WaseemUI scheme, and it doesn't ever
reappear.

(imported from commit 3417fae31fc8d1b87d0d8b463548c24f5c2d260c)

zephyr/static/js/zephyr.js

@@ -540,6 +540,5 @@ $(function () {
     update_autocomplete();
     $('.button-slide').click(function () {
         $('.zephyr_compose').slideToggle('fast');
-        $('.button-slide').hide();
     });
 });