create teardown fixture for tests (#2269)
Closes #2263
Files were being created as a side effect from running tests in
`test_unstructured/metrics/test_evaluate.py`. The added decorator
removes the created directory and its files after the tests run.
Testing
on the main branch, run `make test` or `pytest
test_unstructured/metrics/test_evaluate.py` and files will be created.
On this branch no files are created
