[REF] Update a few references to invoicing

[eileenmcnaughton]

Overview

[REF] Update a few references to invoicing

Before

Legacy access to the invoicing setting

After

Civi::settings()->get('invoicing');

Technical Details

Comments

[civibot]

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[eileenmcnaughton]

@mlutfy I can't quite decide whether to give up on these for now or push through & do them all - but here are a few more

[eileenmcnaughton]

@mlutfy @seamuslee001 @demeritcowboy anyone up to look at this - I feel like it should be just a quick sanity check review

[demeritcowboy]

Sure I can take a look.

[demeritcowboy]

jenkins retest this please (since it's been a while)