Remove trap-door-like logic from shaft traps, since shafts are just

supposed to be holes hidden by debris.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@2337 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on October 5, 2007
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