remove Linux Central from partners list. The website does not work anymore and...

remove Linux Central from partners list. The website does not work anymore and last snapshot in archive.org show "recent additions" CDs from 2011

CVS version numbers

english/partners/2017/partners.data: 1.20 -> 1.21 
english/partners/2017/images/linuxcentral.gif: 1.1 -> 1.2(DEAD)