Thunks/Vulkan: Fix beta extension symbol visibility

[Sonicadvance1]

No description provided.

[Sonicadvance1]

Pretty sure the problem here is that VK_NV_cuda_kernel_launch used to /not/ be a beta extension, but then NVIDIA moved it over to beta. Then instead promoting VK_NVX_binary_import out of beta, but still retaining the NV_NVX prefix instead of VK_NV.

These two extensions are nightmare fuel.

[Sonicadvance1]

Pretty sure my original plan of not supporting any beta extensions still holds here, but this is a special weird one-off backtrack.

[neobrain]

Considering you were fine with disabling these extensions without explicit note before, why don't we just leave all beta extensions (including this one) disabled?

As-is, this PR would complicate updating the interface files since it would make DefinitionsExtract spew out Vulkan functions we don't want, so I'm tentatively -1 on this unless there's a compelling reason to make an exception here.