Revert "placeholder for zuul.wikimedia.org"

Zuul main page is going to be at /zuul/ so this placeholder is no more
needed nor wanted.

This reverts commit 1ca62523f4f4962aab08b3d5253e6ff571c8912f

Change-Id: Idb717e13d9d5b204d0841cb052c40e11b9b1c167