remove unit test parallelization

Author: laurenyu

buildspec-unittests.yml

@@ -18,5 +18,5 @@ phases:
       - start_time=`date +%s`
       - AWS_ACCESS_KEY_ID= AWS_SECRET_ACCESS_KEY= AWS_SESSION_TOKEN=
         AWS_CONTAINER_CREDENTIALS_RELATIVE_URI= AWS_DEFAULT_REGION=
-        tox -e py27,py36,py37,py38 --parallel all -- -n 4 tests/unit
+        tox -e py27,py36,py37,py38 --parallel all -- tests/unit
       - ./ci-scripts/displaytime.sh 'py27,py36,py37,py38 unit' $start_time