simplenode.reltool.config: use default sys-level mod_cond setting

As discussed here
http://erlang.org/pipermail/erlang-questions/2012-December/071135.html
change the reltool spec to use the default sys-level mod_cond setting.
Merge pull request #43 from tuncer/reltool-mod_cond

simplenode.reltool.config: use default sys-level mod_cond setting