Remove wiki.gentoo.org from tests

The test is failing. https://travis-ci.org/WikiTeam/wikiteam/builds/50102997#L546
Might be our fault, but they just updated code:
Tyrian	– (f313f23) 12:47, 23 January 2015	GPLv3+	Gentoo's new web theme ported to MediaWiki.	Alex Legler

I don't think testing screenscraping against a theme used only by Gentoo makes much sense for us.

testing/test_dumpgenerator.py

@@ -68,9 +68,6 @@ class TestDumpgenerator(unittest.TestCase):
             # Gamepedia wikifarm
             ['http://dawngate.gamepedia.com/index.php', 'http://dawngate.gamepedia.com/api.php', u'Spell Vanquish.png'],
             
-            # Gentoo wikifarm
-            ['http://wiki.gentoo.org/index.php', 'http://wiki.gentoo.org/api.php', u'Openclonk screenshot1.png'],
-            
             # Neoseeker wikifarm
             ['http://digimon.neoseeker.com/w/index.php', 'http://digimon.neoseeker.com/w/api.php', u'Ogremon card.png'],