-Fix bugreport:7014 based on Kichi solution (chorus skill wasn't checking partner condition)
--Add kind of handler in skill_check_condition_castbegin for group check and move some from unit unit_skilluse_id2 (wich not really meant for check)
-Cleanup leftover from r17153

git-svn-id: https://rathena.svn.sourceforge.net/svnroot/rathena/trunk@17161 54d463be-8e91-2dee-dedb-b68131a5f0ec