chore: fix tests breaking on main (#3603)
Fix API tests (really more like integration tests) that run only on
main. Also use less compute intensive files to speedup test time and
remove a useless test.
Tests in `test_unstructured/partition/test_api.py` pass, temporarily
running outside of main per per screenshot:
https://github.com/Unstructured-IO/unstructured/actions/runs/10754098974/job/29824415513
