handle 404 in delete from bucket

[jonasfj]

DetailedApiRequestError(status: 404) should be handled in BucketExt.deleteWithRetry where it can safely be ignored.

api_builder: Unhandled error in API handler (incidentId: 735a3142-68b7-40c9-8321-82dbcc733bec)

Error:
    DetailedApiRequestError(status: 404, message: No such object: dartlang-pub-canonical-packages/packages/XXXXXXXXXX)

Stack:
    #0      validateResponse (package:_discoveryapis_commons/src/api_requester.dart:306:9)
    <asynchronous suspension>
    #1      ApiRequester.request (package:_discoveryapis_commons/src/api_requester.dart:72:16)
    <asynchronous suspension>
    #2      ObjectsResource.delete (package:googleapis/storage/v1.dart:3323:5)
    <asynchronous suspension>
    #3      RetryOptions.retry (package:retry/retry.dart:131:16)
    <asynchronous suspension>
    #4      _retry (package:pub_dev/shared/storage.dart:269:10)
    <asynchronous suspension>
    #5      BucketExt.deleteWithRetry (package:pub_dev/shared/storage.dart:107:12)
    <asynchronous suspension>
    #6      TarballStorage.deleteArchiveFromAllBuckets (package:pub_dev/package/tarball_storage.dart:179:5)
    <asynchronous suspension>
    #7      PackageBackend.removePackageTarball (package:pub_dev/package/backend.dart:1659:5)
    <asynchronous suspension>
    #8      Pool.withResource (package:pool/pool.dart:127:14)
    <asynchronous suspension>
    #9      Future.wait.<anonymous closure> (dart:async/future.dart:528:21)
    <asynchronous suspension>
    #10     AdminBackend._removePackage (package:pub_dev/admin/backend.dart:333:5)
    <asynchronous suspension>
    #11     AdminBackend.removePackage (package:pub_dev/admin/backend.dart:304:5)
    <asynchronous suspension>