Remove "drifitng" mutation, since consensus seems to be that it wasn't

very good.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3083 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on December 17, 2007
POKKD4OOQZD4PMEITE5SNPXBNRJNNEJ5DJLRHF5PSF4G4MCYFM3AC
Change contents