chore(frontends/lean/proof_qed_elaborator): remove obsolete comment
chore(frontends/lean/proof_qed_elaborator): remove obsolete comment

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

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