More changes required to eliminate pylint warnings

[martinholmer]

Changes are cosmetic rather than substantive.

While looking at pylint warnings genratred by the tmd/utils/is_tax_filer.py code, I discovered that the is_tax_filer function is not called anywhere in the TMD repo code. So, I added at comment indicating that fact (rather than removing the module).

[donboyd5]

Thank you, @martinholmer. I believe it will be potentially useful, sometime in the future, to examine that module carefully, update it as needed, and implement it. It could enable us to make modest improvements to how we target data. Doing that might be far in the future, but it's worth retaining the module, as you have done.