Fixes CODAGT-175
Addresses a review finding in https://github.com/coder/coder/pull/23827
that the nil-guards for both `database.Store` and `chatID` are both dead
code in practice in the `chattool` package.
- Modifies the return signatures require passing both `database.Store`
and `chatID` explicitly as positional arguments instead of just
parameter struct keys.
- Drops the nil-guards for `database.Store` and `chatID`.
Cian Johnston
a74015fc85