Setting::getItem - use deprecatedWarning instead of just logging

[demeritcowboy]

Overview

I don't think this will change anything in core, but let's see if anything comes up in tests.

[civibot]

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[eileenmcnaughton]

Yeah I guess those would fail - we can remove those tests now

[demeritcowboy]

Is there still value in testing civicrm_setting overrides for core and custom settings? I've updated the test so it still does that.

[eileenmcnaughton]

@demeritcowboy I think there is still value in testing the functionality - but via Civi::setting()->get() or the api

[demeritcowboy]

Ok updated.