FSA: Add cleanup to GetDirectory tests
These tests are leaving behind files in the root of the Bucket File
System. This causes flakiness in other WPTs that expect a clean
directory.
This CL adds a cleanup function to remove the files they create.
Bug: 363601806
Change-Id: Icaae990a0e231a3569aead79a763f48bcd1caba3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5842591
Commit-Queue: Nathan Memmott memmott@chromium.org
Reviewed-by: Christine Hollingsworth christinesm@chromium.org
Cr-Commit-Position: refs/heads/main@{#1352335}