Fixes #32610. Closes #32614.

Lua scripts in redis are *blocking*, meaning that no other client can
execute any commands while the script is running. See
https://redis.io/commands/eval#atomicity-of-scripts.

This results in the following exceptions once the number of keys is
sufficiently large:

    BUSY Redis is busy running a script.
    You can only call SCRIPT KILL or SHUTDOWN NOSAVE.

This commit replaces the lua-based implementation with one that uses
`SCAN` and `DEL` in batches. This doesn't block the server.

The primary limitation of `SCAN`, i.e. potential duplicate keys, is of
no consequence here, because `DEL` ignores keys that do not exist.