Redundant textures in output after specular gloss -> metal rough conversion

[marpe]

I noticed that after the conversion of the spec gloss textures to metal rough that they still are present in the output

Here's the sheets compared between 1.5.0 and 1.6.0 when running glTF-Toolkit/glTF-Toolkit.Test/Resources/gltf/WaterBottle/WaterBottle.gltf. The spec gloss textures are still present in the textures/images arrays in 1.6.0 (indices: 0, 1, 5, 6).

[najadojo]

Thanks for opening this issue. There have been a handful of requests to optimize the result. These include removing unused textures, and de-duplicating textures and meshes. We haven't had an opportunity to address these issues but pull requests would certainly be welcome.