Simplify TSO halo management. Since backlit() now takes the halo into

account, there's no need to manually backlight invisible monsters anymore.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@4341 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on April 18, 2008
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