[llvm] [AMDGPU][NFC] Function decls no longer required in tests. (PR #96632)

[Pravin Jagtap via llvm-commits]

pravinjagtap wrote:

* **#96632** <a href="https://app.graphite.dev/github/pr/llvm/llvm-project/96632?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a> 👈
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https://github.com/llvm/llvm-project/pull/96632