Making the admin/statistics.php obsolete and getting admin/users/statistics.php
to do the work.

The institution 'all' shows the site statistics

Sponsored by University of Sussex and Dublin City University

behatnotneeded

Change-Id: Ic2fb9d4ef355fdc5e5527c1ce776463d821c0c08
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>