message: fix(c-api) Simplify `NonNull<T>` by `&T`.
diff: use super::super::value::wasm_valkind_t;
  use std::convert::TryInto;
  -use std::ptr::NonNull;
  use wasmer::ValType;
  #[allow(non_camel_case_types)]
  @@ -84,11 +83,8 @@ pub extern "C" fn wasm_valtype_new(kind: wasm_valkind_t) -> Option<Box<wasm_valt
  pub unsafe extern "C" fn wasm_valtype_delete(_valtype: Option<Box<wasm_valtype_t>>) {}
  #[no_mangle]
  -pub unsafe extern "C" fn wasm_valtype_kind(
  - valtype: Option<NonNull<wasm_valtype_t>>,
  -) -> wasm_valkind_t {
  +pub unsafe extern "C" fn wasm_valtype_kind(valtype: Option<&wasm_valtype_t>) -> wasm_valkind_t {
  valtype
  .expect("`wasm_valtype_kind: argument is a null pointer")
  - .as_ref()
  .valkind as wasm_valkind_t
  }
  