[REF] Move more functions back to pdfLetter class

[eileenmcnaughton]

Overview

[REF] Move more functions back to pdfLetter class

Before

Form processing 'spread' across 2 classes

After

Consolidated onto one

Technical Details

As with the previous moves this is

1. covered by unit tests
2. just code moving around

But note that this doesn't move whole functions but moves the
contents of postProcess & buildQuickForm back into the same functions
on the 'actual' class

Comments

[civibot]

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[colemanw]

This looks like reasonable cleanup.