chore: fixed std wasm build of xcm (#2535)

# Description

just ensures

```sh
cargo check --package staging-xcm  --no-default-features  --target wasm32-unknown-unknown --features=std
```

work (for CosmWasm)

# Checklist

- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [ ] My PR follows the [labeling requirements](CONTRIBUTING.md#Process)
of this project (at minimum one label for `T`
  required)
- [x] I have made corresponding changes to the documentation (if
applicable)
- [ ] I have added tests that prove my fix is effective or that my
feature works (if applicable)

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/primitives/weights/src/lib.rs

@@ -27,6 +27,7 @@ extern crate self as sp_weights;
 mod weight_meter;
 mod weight_v2;
 
+use bounded_collections::Get;
 use codec::{CompactAs, Decode, Encode, MaxEncodedLen};
 use scale_info::TypeInfo;
 #[cfg(feature = "serde")]
@@ -36,7 +37,6 @@ use sp_arithmetic::{
 	traits::{BaseArithmetic, SaturatedConversion, Unsigned},
 	Perbill,
 };
-use sp_core::Get;
 use sp_debug_derive::RuntimeDebug;
 
 pub use weight_meter::*;
@@ -270,7 +270,7 @@ pub type NoFee<T> = FixedFee<0, T>;
 /// # Example
 ///
 /// ```
-/// # use sp_core::ConstU128;
+/// # use bounded_collections::ConstU128;
 /// # use sp_weights::ConstantMultiplier;
 /// // Results in a multiplier of 10 for each unit of weight (or length)
 /// type LengthToFee = ConstantMultiplier::<u128, ConstU128<10u128>>;
@@ -360,7 +360,7 @@ mod tests {
 
 	#[test]
 	fn constant_fee_works() {
-		use sp_core::ConstU128;
+		use bounded_collections::ConstU128;
 		assert_eq!(
 			ConstantMultiplier::<u128, ConstU128<100u128>>::weight_to_fee(&Weight::zero()),
 			0