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

licenses/aioredis.txt

@@ -1,22 +0,0 @@
-The MIT License (MIT)
-
-Copyright (c) 2014-2017 Alexey Popravka
-Copyright (c) 2021 Sean Stewart
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.