(bug 46682) Drop doc mention of removed importUseModWiki.php script

The script was removed in commit f51b580f0c7ee63539e16d3017f8dd0de0ee2391
(October 2011) due to lack of maintenance.

Bug: 46682
Change-Id: Ida8369d4ad9326664b072adb0cb73f2f24465d1e