Remove phpredis functionMap entries without better types than the stubs

Kept entries that have __benevolent<> return types or more precise
array types than the phpstorm-stubs. The removed ones only had types
from phpredis 4/5 docs, often narrower than what phpredis 6 declares
(e.g. RedisCluster::del() returning int instead of
RedisCluster|int|false), wider, or contradicting it.

Methods that previously returned mixed because of an empty return type
in the entry, and whose phpredis 6 return type is a union, now return
it as __benevolent<> so they do not start reporting errors.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WfLkuAJxafghcVbf9HxEwu

Author: ondrejmirtes