Remove duplicate circe json codec

[notthatbreezy]

Overview

This removes a duplicate codec for TileLayout - there is already one here and it is really easy to get in a situation where both are available and hit an ambiguous implicit error.

Checklist

• docs/CHANGELOG.rst updated, if necessary

[pomadchin]

Ah, it looks like you also need to sign ECA, could you do it if it is not hard for you?

If you have / once you'll have a signed ECA you can sign your commit via
git commit --amend -s && git push origin -f feature/cmb/remove-duplicate-json-codec

[notthatbreezy]

@pomadchin Updated PR and signed ECA

I also added a commit that removed the private restriction on an overload for reading tiff tags -- this wasn't in previous versions of GT and RF uses this method and another project now.

[pomadchin]

Thank Chris! Looks good to me, merging once Travis is happy; and after updating the changelog :d

[notthatbreezy]

Changelog updated!

[pomadchin]

@notthatbreezy perfect, thanks!