Drop StrictRedis references in aioredis v2

[connebs]

StrictRedis is a legacy class in redis-py that is there only for backwards compatiability with versions of redis-py before 3.x. However since aioredis v2 based on redis-py has just been released and never has and never will support versions of redis-py < 3.x, it doesn't really make sense to include StrictRedis in the aioredis API, as it is literally just an alias to the Redis class.

Said simply: there is no reason anyone integrating aioredis-py@2.x should be using StrictRedis, and a clear reason not to use it (it will maybe/probably be dropped from redis-py in a future major version).

As it is, its presence in the library can only cause confusion and does not provide any benefit.