Update isvwiki to CC BY-SA 4.0 (#5259)

Since Wikimedia Foundation projects are also under CC BY-SA 4.0 now, we
can update the licence in our Interslavic wiki so we continue to be
compatible.

Creative Commons licences allow upgrade of the versions, see
https://meta.wikimedia.org/wiki/Terms_of_use/Creative_Commons_4.0/Legal_note

Previously, our community downgraded the licence to CC BY-SA 3.0 because
of potential legal complications:
https://isv.miraheze.org/wiki/Topic:Ul5tedyf4bbjlok2

LocalSettings.php

@@ -2419,7 +2419,6 @@
 		'glitchcitywiki' => 'Creative Commons Attribution-NonCommercial 3.0 Unported (CC BY-NC 3.0)',
 		'googologywiki' => 'Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)',
 		'incubatorwiki' => 'Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)',
-		'isvwiki' => 'Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)',
 		'jadtechwiki' => 'Copyright © Jak and Daxter Technical Wiki. All rights reserved.',
 		'militarywiki' => 'Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)',
 		'privadowiki' => 'Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)',
@@ -2443,7 +2442,6 @@
 		'glitchcitywiki' => 'https://creativecommons.org/licenses/by-nc/3.0',
 		'googologywiki' => 'https://creativecommons.org/licenses/by-sa/3.0',
 		'incubatorwiki' => 'https://creativecommons.org/licenses/by-sa/3.0',
-		'isvwiki' => 'https://creativecommons.org/licenses/by-sa/3.0',
 		'jadtechwiki' => 'https://jadtech.miraheze.org/wiki/MediaWiki:Copyright',
 		'militarywiki' => 'https://creativecommons.org/licenses/by-sa/3.0',
 		'privadowiki' => 'https://creativecommons.org/licenses/by-sa/3.0',