[MLIR][FuncToLLVM] Remove typed pointers from call conversion test pass (#71107)

This commit removes typed pointers from the Func to LLVM test pass.
Typed pointers have been deprecated for a while now and it's planned to
soon remove them from the LLVM dialect.

Related PSA:
https://discourse.llvm.org/t/psa-removal-of-typed-pointers-from-the-llvm-dialect/74502