Revert "Disable `f16` on Aarch64 without `neon`"

The LLVM issue [1] was resolved and the fix was synced to rust-lang/rust
in [2].

This reverts commit c51b229140c885cac757a405a328a07e90d5bca9.

[1]: https://github.com/llvm/llvm-project/issues/129394
[2]: https://github.com/rust-lang/rust/pull/138695