fix(frontends/lean): remove keywords 'class' and '[class]'
fix(frontends/lean): remove keywords 'class' and '[class]'

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

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