feat(data/set/finite): remove exists_finset_of_finite (#1782)
feat(data/set/finite): remove exists_finset_of_finite (#1782)

* feat(data/set/finite): remove exists_finset_of_finite

exists_finset_of_finite is a duplicate of finite.exists_finset_coe
At same time, provide a `can_lift` instance to lift sets to finsets.

* Add docstring

leanprover-community/mathlib,leanprover-community/mathlib