Outdated KTX info

[JMS55]

In section https://docs.vulkan.org/tutorial/latest/15_GLTF_KTX2_Migration.html#_optimizing_ktx2_files

It suggests to do

toktx --format BC7_RGBA texture.ktx2 texture.png

However --format no longer exists, and I believe toktx in general is deprecated in favor of ktx create.