Don't count `requirements` in "contracts checked" count

[obycode]

clarinet check reports the number of contracts checked, e.g.:

✔ 2 contracts checked

This number should not include contracts from requirements.

Using the same project from #394 (below), this should show 1 contract checked, but it reports 2.

contracts/bug.clar:

(use-trait nft-trait 'SP2PABAF9FTAJYNFZH93XENAJ8FVY99RRM50D2JG9.nft-trait.nft-trait)
42 ;; this is here to avoid https://github.com/hirosystems/clarity-repl/issues/109

Clarinet.toml:

[project]
name = "check-required"

[[project.requirements]]
contract_id = "SP2PABAF9FTAJYNFZH93XENAJ8FVY99RRM50D2JG9.nft-trait"

[contracts.bug]
path = "contracts/bug.clar"