refactor(algebraic_geometry/structure_sheaf): Remove redundant isomorphism (#7410)
refactor(algebraic_geometry/structure_sheaf): Remove redundant isomorphism (#7410)

Removes `stalk_iso_Type`, which is redundant since we also have `structure_sheaf.stalk_iso`, which is the same isomorphism in `CommRing`





leanprover-community/mathlib,leanprover-community/mathlib