Stale chunks might be there because a file was removed or would just not
be uploaded, for any reason.
We just start the DeleteJob but we don't care if it success or not.
Relates to https://github.com/owncloud/core/issues/26981
One of the test is testing the case where the file is modified on the server
during the upload. So this test the precondition failed error.
The FakeGetReply logic was modified because resizing a 150MB big QByteArray
by increment of 16k just did not scale when downloading a big file.
Relates to https://github.com/owncloud/core/issues/26981
We do not track the success or error of the DeleteJob because it does not
matter. If it fails, it might be because the chunks were already removed.
If not, the chunks will be stale, but the server must anyway do a few
cleanup from time to time because we do not always remove the chunks
