This has been implemented as of botocore v1.11.0
See the Upgrade notes.

Botocore currently vendors a fairly dated version of requests. This particular version of requests also vendors the urllib3 library. We originally vendored requests to give us more control over the specific version that was being used as we need to make changes to some of the behavior provided by both requests (redirect behavior, etc.) and urllib3 (HTTP 100-continue support). By dropping requests and using urllib3 directly we gain more control over our HTTP client behavior and simplify our dependencies.

Let's use this issue as an aggregate issue to contain discussion around unvendoring requests and switching to using urllib3 directly.

Implementation: #1495

Related Issues:
aws/aws-cli#2994
#1258
#1248
#756
#1370
#1466
#1300
#1385
#1464