CSV Export: Add deprecation warning

[eileenmcnaughton]

Overview

Adds a deprecation warning on code I believe to be unreachable

Before

After

A deprecation message would show up (on dev sites) if this code is ever hit

Technical Details

On digging into this export function I cannot find any way to access these lines.

If no-one else can spot a way I propose adding a deprecation notice & later removing

Comments

[civibot]

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[mlutfy]

Merge based on code review, and quick look at the code. I am not sure I understand the code, and the deprecation warning will help us understand/cleanup.

[eileenmcnaughton]

Lol - I'm sure I don't understand the code :-)