test_decorators: Remove cachify test cases.
test_decorators: Remove cachify test cases.

cachify has been removed in 9d448e73d2c3b7f2983f239a24e2d45ec9704904.
We don't need to keep its tests.

TODO: functools.lru_cache can be replaced by functools.cache when we
drop Python 3.8.

Signed-off-by: Zixuan James Li <74923aee05c23ca90566381b5d6b0cd9451b6054@gmail.com>

zulip/zulip,andersk/zulip,rht/zulip,zulip/zulip,rht/zulip,zulip/zulip,zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,zulip/zulip,rht/zulip,andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip