evolve: use obsutil._getobsfate() directly
It's been there since 4.5 (265cd9e19d26), we can safely rely on it.
It's necessary though to use the correct spelling of superseded.
#!/bin/sh
set -eu
case $1 in
default)
echo default
;;
mercurial-*)
exp=$(echo "$1" | cut -d- -f2 | sed 's#\.#\\.#g')
echo 'max(tag("re:^'"$exp"'"))'
;;
*)
echo stable
;;
esac