Removes portal-url, currentevents-url and helppage from default Sidebar

portal-url ("Community portal"), currentevents-url ("Current events") 
and helppage ("Help") lead to empty pages in a fresh MediaWiki install, 
when most projects won't need these pages ever. Removing the 
corresponding lines.

Bug 53862
Change-Id: Icb0e1b91e40bd682629f8a6f7291dbf8588b586b
Merge "Removes portal-url, currentevents-url and helppage from default Sidebar"