Remove references to 'key' option
Remove references to 'key' option

This was introduced in f24142da4e2237e39c9a98d6de0b3665fcf95db9 (#676).

It is part of a future improvement to the Memcache library, that should
not have been merged into the 5.22 release [1].

[1]: https://github.com/ADOdb/ADOdb/pull/816#issuecomment-1076967876

ipso/ADOdb,ipso/ADOdb