vulkan: fix GPU deduplication logic. (llama/19222)

vulkan: fix GPU deduplication logic. (llama/19222)

* vulkan: fix GPU deduplication logic.

As reported in https://github.com/ggml-org/llama.cpp/issues/19221, the
(same uuid, same driver) logic is problematic for windows+intel igpu.

Let's just avoid filtering for MoltenVK which is apple-specific, and
keep the logic the  same as before 88d23ad5 - just dedup based on UUID.

Verified that MacOS + 4xVega still reports 4 GPUs with this version.

* vulkan: only skip dedup when both drivers are moltenVk