undo part of r1.231 -> 1.232 patch, which changed default value of relationship_graphs to ON. We can't do this as not all users will have graphviz/wingraphviz installed.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3202 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9