refactor(data/finsupp/basic): remove sub lemmas (#9603)
* Remove the finsupp sub lemmas that are special cases of lemmas in `algebra/order/sub`, namely:
* `finsupp.nat_zero_sub`
* `finsupp.nat_sub_self`
* `finsupp.nat_add_sub_of_le`
* `finsupp.nat_sub_add_cancel`
* `finsupp.nat_add_sub_cancel`
* `finsupp.nat_add_sub_cancel_left`
* `finsupp.nat_add_sub_assoc`
* Rename the remaining lemmas to use `tsub`:
* `finsupp.coe_nat_sub` → `finsupp.coe_tsub`
* `finsupp.nat_sub_apply` → `finsupp.tsub_apply`
Lemmas in `algebra/order/sub` will soon also use `tsub` (see [Zulip](https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/mul_lt_mul''''))
