Remove inaccurate comment and unneeded code in monsters::body_weight().

Water elementals aren't insubstantial, and should have their weight set to 1500 by virtue of their size, so there's no need to hardcode it there.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@4884 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on May 5, 2008
ENQHQXU7GQHWS75W7G3NXWEJJ45QBC6GZ5CFRA5T26SPQFPKZEYAC
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