Unpin channels-redis (#15329) (#6647)

* unpin channels-redis

The bug that initially caused the upgrade block has been resolved https://github.com/django/channels_redis/issues/332

* replace aioredis Exception with a redis Exception

Version 4.0.0 of channel-redis migrated the underlying Redis library from aioredis to redis-py. The Exception has been changed to an equivalent

* remove unused license

* remove UPGRADE BLOCKER in README

* remove hiredis

it was an indirect dependency from aioredis which was removed

* remove unused license

* add back hiredis

it's potentially providing a performance boost. install explicitly as a part of redis. upgrade to more recent version

* remove UPGRADE BLOCKER for hiredis

it was also addressed as a part of this PR

requirements/README.md

@@ -120,24 +120,6 @@ in the top-level Makefile.
 
 If modifying this library make sure testing with the offline build is performed to confirm it is functionally working.
 
-### channels-redis
-
-Due to an upstream bug (linked below), we see `RuntimeError: Event loop is closed` errors with newer versions of `channels-redis`.
-Upstream is aware of the bug and it is likely to be fixed in the next release according to the issue linked below.
-For now, we pin to the old version, 3.4.1
-
-* https://github.com/django/channels_redis/issues/332
-* https://github.com/ansible/awx/issues/13313
-
-### hiredis
-
-The hiredis 2.1.0 release doesn't provide source distribution on PyPI which prevents users to build that python package from the
-sources.
-Downgrading to 2.0.0 (which provides source distribution) until the channels-redis issue is fixed or a newer hiredis version is
-available on PyPi with source distribution.
-
-* https://github.com/redis/hiredis-py/issues/138
-
 ## Library Notes
 
 ### pexpect