Fix two formula leaks.

* src/ltlvisit/simplify.cc (reduce_sere_ltl): Here.
* src/ltltest/reduccmp.test: Add a test case.

src/ltltest/reduccmp.test

@@ -329,6 +329,7 @@ for x in ../reduccmp ../reductaustr; do
      run 0 $x '{a;(b[*2..4];c*;([*0]+{d;e}))*}!' \
               '{a;(b[*2..4];c*;([*0]+{d;e}))*}!'
      run 0 $x '{((a*;b)+[*0])[*4..6]}!' '{((a*;b))[*0..6]}!'
+     run 0 $x '{c[*];e[*]}[]-> a' '{c[*];e[*]}[]-> a'
      ;;
   esac