ltsmin: placement new requires placement delete

This commit fixes a bug that (randomly) occurs when
calling destructor of kripkecube.

*  spot/ltsmin/spins_kripke.hxx: here.

spot/ltsmin/spins_kripke.hxx

@@ -266,6 +266,7 @@ namespace spot
         delete inner_[i].compressed_;
         delete inner_[i].uncompressed_;
       }
+    ::operator delete(manager_);
     delete[] inner_;
   }