Revert "change: install python-dateutil explicitly for botocore (#81)" (#88)

This reverts commit e7fa17b.

Author: laurenyu

tox.ini

@@ -46,9 +46,7 @@ passenv =
     AWS_DEFAULT_REGION
 # {posargs} can be passed in by additional arguments specified when invoking tox.
 # Can be used to specify which tests to run, e.g.: tox -- -s
-# TODO: Remove pip install python-dateutil==2.8.0 once botocore no longer requires a pinned version
 commands =
-    pip install python-dateutil==2.8.0
     coverage run --rcfile .coveragerc_{envname} --source sagemaker_mxnet_serving_container -m pytest {posargs}
     {env:IGNORE_COVERAGE:} coverage report --fail-under=90 --include *sagemaker_mxnet_serving_container*
 deps = .[test]