build: We're already upgraded to 4.x

So pinning to a minor version under 4.x is weird.  THe only breaking
change that is in the changelogs is at 4.7 with a change that doesn't
affect this repo.

Breaking Change: https://pymongo.readthedocs.io/en/stable/changelog.html#id7
Changelog: https://pymongo.readthedocs.io/en/stable/changelog.html#changelog

requirements/base.in

@@ -3,8 +3,7 @@
 -c constraints.txt
 
 django
-# https://pymongo.readthedocs.io/en/4.4.0/migrate-to-pymongo4.html#son-items-now-returns-dict-items-object
-pymongo>=4.0.0,<4.4.1
+pymongo>=4.0.0
 pytz
 six
 celery