cli: remove ssl cert warning

[half-duplex]

Description

I missed this in #2278 😐
Since ca_certs=None is now valid, the warning is nonsense. If the setting is truly invalid, Sopel will quit with an exception:

ValueError: Invalid value for core.ca_certs: Value must be an existing or creatable file.

or

ssl.SSLError: [X509: NO_CERTIFICATE_OR_CRL_FOUND] no certificate or crl found (_ssl.c:4123)

(Though after the latter, it'll still attempt to reconnect after shutting down??)

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches

[dgw]

(Though after the latter, it'll still attempt to reconnect after shutting down??)

Some weird lifecycle stuff happening, maybe. That should be at least caught, but attrs like hasquit are still a bit wonky. Good for another patch if you fall into that rabbit hole.

[dgw]

I believe #2306 touches some stuff that will fix trying to reconnect after SSL failure, so there's no need to block this on it.

[half-duplex]

(Also, this doesn't affect the result, just removes the nonsense message preceding it)

[dgw]

(Should it be relabeled as a Tweak or Housekeeping instead of Bugfix?)

[half-duplex]

I figure telling the user something outright incorrect counts as a bug. Not quitting is more or less unrelated.

[dgw]

Exirel agreeing with me on IRC was enough to push me into "this isn't a bug" territory. (More of a record-keeping thing than any kind of defense. Just didn't like leaving the thread dangling like that after the label change.)