chore(util/sexpr): cleanup
chore(util/sexpr): cleanup

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

soonhokong/lean-windows,digama0/lean,c-cube/lean,UlrikBuchholtz/lean,soonhokong/lean-osx,UlrikBuchholtz/lean,javra/lean,soonhokong/lean,sp3ctum/lean,c-cube/lean,digama0/lean,fpvandoorn/lean2,leanprover/lean,levnach/lean,fpvandoorn/lean,leanprover-community/lean,eigengrau/lean,digama0/lean,avigad/lean,sp3ctum/lean,fpvandoorn/lean,johoelzl/lean,eigengrau/lean,leanprover-community/lean,dselsam/lean,sp3ctum/lean,htzh/lean,leanprover/lean,rlewis1988/lean,c-cube/lean,UlrikBuchholtz/lean,soonhokong/travis_test,Kha/lean,johoelzl/lean,fgdorais/lean,soonhokong/lean,sp3ctum/lean,leanprover/lean,dselsam/lean,UlrikBuchholtz/lean,rlewis1988/lean,javra/lean,leanprover-community/lean,fpvandoorn/lean2,eigengrau/lean,javra/lean,fpvandoorn/lean,leodemoura/lean,sp3ctum/lean,digama0/lean,leanprover/lean,leanprover-community/lean,dselsam/lean,digama0/lean,soonhokong/lean-osx,fpvandoorn/lean,Kha/lean,javra/lean,avigad/lean,leanprover-community/lean,johoelzl/lean,soonhokong/travis_test,c-cube/lean,htzh/lean,dselsam/lean,c-cube/lean,rlewis1988/lean,avigad/lean,fpvandoorn/lean2,Kha/lean,Kha/lean,fpvandoorn/lean2,fpvandoorn/lean,soonhokong/lean-osx,Kha/lean,eigengrau/lean,dselsam/lean,soonhokong/lean-windows,levnach/lean,leodemoura/lean,soonhokong/travis_test,soonhokong/lean-osx,rlewis1988/lean,htzh/lean,UlrikBuchholtz/lean,johoelzl/lean,levnach/lean,soonhokong/lean,soonhokong/lean-windows,eigengrau/lean,soonhokong/lean,avigad/lean,soonhokong/lean-windows,fgdorais/lean,johoelzl/lean,Kha/lean,fgdorais/lean,fpvandoorn/lean,avigad/lean,soonhokong/lean-osx,avigad/lean,johoelzl/lean,dselsam/lean,leodemoura/lean,levnach/lean,leodemoura/lean,rlewis1988/lean,leodemoura/lean,javra/lean,leanprover/lean,leanprover/lean,leanprover-community/lean,soonhokong/lean-windows,fgdorais/lean,soonhokong/lean,levnach/lean,digama0/lean,fgdorais/lean,htzh/lean,fgdorais/lean,rlewis1988/lean,soonhokong/travis_test,leodemoura/lean,fpvandoorn/lean2,htzh/lean