REF Cleanup ReCAPTCHA code

[mattwire]

Overview

This is a refactor in preparation for moving the reCAPTCHA code to the new reCAPTCHA extension for the campaign signature form.
See https://lab.civicrm.org/dev/core/-/issues/2571

Before

More complex, old code patterns.

After

Simpler, current code patterns.

Technical Details

This switches from using the $config object to retrieve settings via magic properties and uses the Civi::settings() functions.

Comments

[civibot]

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[eileenmcnaughton]

@demeritcowboy this looks right to me - are all your concerns addressed?

[demeritcowboy]

I hadn't run it but codewise looked good.

[eileenmcnaughton]

I think this is simple enough / readable enough as a change that I'm going to merge without having r-run