Update Vulkan dependency docs

[JeremyRand]

Vulkan deps are optional. vulkan-utils is replaced with vulkan-tools since Debian 10.

[tencent-adm]

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[nihui]

Yeah
With simplevk enabled by default in the next release, the vulkan sdk is no longer needed. We will most likely need to update the documentation :D

[nihui]

Thanks for your contribution !