Remove foreachwiki_populate_categories.php

This didn't work.  Instead, we just ran:

sudo -u apache foreachwikiindblist /a/common/gettingstarted-with-category-suggestions.dblist GettingStarted/maintenance/populate_categories.php

Change-Id: I33c22234d3c19683f6c66aedf585854623e7ce59
Merge "Remove foreachwiki_populate_categories.php"