Elide "do nothing" custom functions

[AsherGlick]

This requires a little bit of consideration for how the yaml frontmatter should be formatted, but we currently have a case where we are not writing to a protobin field but we still have that field referenced in the frontmatter. Though no reads or writes ever occur to the field it still needs to be present in the proto schema because we still generate accessory functions that just pass into a null function.

We should change the generator the the yaml docs as needed to be able to remove that field from the proto schema.