chore(frontends/lean): code cleanup
chore(frontends/lean): code cleanup

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

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