[llvm] [RISCV] Remove intrinsic declarations in tests, NFC (PR #167474)

[Yueh-Ting Chen via llvm-commits]

eopXD wrote:

I think what @arsenm means is that compiler with `clang -emit-llvm` still emits the declaration, and a batch-update to all existing test cases will still add back those declarations you are trying to remove here. So probably need to fix somewhere for the declaration gen.

https://github.com/llvm/llvm-project/pull/167474