fix(frontends/lean/elaborator): visit_prenum was creating unnecessary universe metavariable
fix(frontends/lean/elaborator): visit_prenum was creating unnecessary universe metavariable

This was creating problems for the new type class resolution procedure
since visit_prenum was also not creating any constraint that enforced
the universe level of A to be equal to the superfluous universe level.

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