Revert fileapi_entry_test to use unittest.dart
Revert fileapi_entry_test to use unittest.dart

Bug: https://github.com/dart-lang/sdk/issues/40659

This behavior is similar to other tests where removing the dependency on
unittest leads to unhandled rejections.

Change-Id: Iba9eed271b839c764e544cc7200a132f0fb8e92b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136480
Reviewed-by: Sigmund Cherem <beaea8fd7d2a56555046ba4f362c8a93e3938576@google.com>
Commit-Queue: Srujan Gaddam <4175f2f2dd3cde6c8ffb10fc9674dc09abf813fe@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk