au_test_harness: Remove leftover code that is causing issues

This was mistakenly leftover from CL:1828293

BUG=chromium:1010372
TEST=./cros_au_test_harness.py --board=betty --type=vm  --no_graphics --verbose --target_image=/home/ahassani/trunk/images/betty/chromiumos_qemu_image.bin --test_results_root=/home/ahassani/chroot/tmp/test-me --verify_suite_name=smoke  --test_prefix=SimpleTestVerify --ssh_private_key=/home/ahassani/trunk/chromite/ssh_keys/testing_rsa

Exempt-From-Owner-Approval: The change is trivial and we want to get
paladin builders green ASAP.

Change-Id: I6856e8a49394e8b73b32f595efcd480d17aadee4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/1834746
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Jason Clinton <jclinton@chromium.org>
diff --git a/au_test_harness/au_worker.py b/au_test_harness/au_worker.py
index 063b83b..01b59f6 100644
--- a/au_test_harness/au_worker.py
+++ b/au_test_harness/au_worker.py
@@ -27,7 +27,6 @@
     self.test_results_root = test_results_root
     self.all_results_root = os.path.join(test_results_root, 'all')
     self.fail_results_root = os.path.join(test_results_root, 'failed')
-    self.use_delta_updates = options.delta
     self.verbose = options.verbose
     self.vm_image_path = None
     self.verify_suite = 'suite:%s' % (options.verify_suite_name or 'smoke')