[FRAME] Warn on unchecked weight witness (#1818)

Adds a warning to FRAME pallets when a function argument that starts
with `_` is used in the weight formula.
This is in most cases an error since the weight witness needs to be
checked.

Example:

```rust
#[pallet::call_index(0)]
#[pallet::weight(T::SystemWeightInfo::remark(_remark.len() as u32))]
pub fn remark(_origin: OriginFor<T>, _remark: Vec<u8>) -> DispatchResultWithPostInfo {
	Ok(().into())
}
```

Produces this warning:

```pre
warning: use of deprecated constant `pallet::warnings::UncheckedWeightWitness_0::_w`: 
                 It is deprecated to not check weight witness data.
                 Please instead ensure that all witness data for weight calculation is checked before usage.
         
                 For more info see:
                     <https://github.com/paritytech/polkadot-sdk/pull/1818>
   --> substrate/frame/system/src/lib.rs:424:40
    |
424 |         pub fn remark(_origin: OriginFor<T>, _remark: Vec<u8>) -> DispatchResultWithPostInfo {
    |                                              ^^^^^^^
    |
    = note: `#[warn(deprecated)]` on by default
```

Can be suppressed like this, since in this case it is legit:

```rust
#[pallet::call_index(0)]
#[pallet::weight(T::SystemWeightInfo::remark(remark.len() as u32))]
pub fn remark(_origin: OriginFor<T>, remark: Vec<u8>) -> DispatchResultWithPostInfo {
	let _ = remark; // We dont need to check the weight witness.
	Ok(().into())
}
```

Changes:
- Add warning on uncheded weight witness
- Respect `subkeys` limit in `System::kill_prefix`
- Fix HRMP pallet and other warnings
- Update`proc_macro_warning` dependency
- Delete random folder `substrate/src/src` 🙈 
- Adding Prdoc

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

substrate/frame/elections-phragmen/src/benchmarking.rs

@@ -379,7 +379,7 @@ benchmarks! {
 		let root = RawOrigin::Root;
 	}: _(root, v, d)
 	verify {
-		assert_eq!(<Voting<T>>::iter().count() as u32, 0);
+		assert_eq!(<Voting<T>>::iter().count() as u32, v - d);
 	}
 
 	election_phragmen {

substrate/frame/elections-phragmen/src/lib.rs

@@ -591,15 +591,18 @@ pub mod pallet {
 		/// ## Complexity
 		/// - Check is_defunct_voter() details.
 		#[pallet::call_index(5)]
-		#[pallet::weight(T::WeightInfo::clean_defunct_voters(*_num_voters, *_num_defunct))]
+		#[pallet::weight(T::WeightInfo::clean_defunct_voters(*num_voters, *num_defunct))]
 		pub fn clean_defunct_voters(
 			origin: OriginFor<T>,
-			_num_voters: u32,
-			_num_defunct: u32,
+			num_voters: u32,
+			num_defunct: u32,
 		) -> DispatchResult {
 			let _ = ensure_root(origin)?;
+
 			<Voting<T>>::iter()
+				.take(num_voters as usize)
 				.filter(|(_, x)| Self::is_defunct_voter(&x.votes))
+				.take(num_defunct as usize)
 				.for_each(|(dv, _)| Self::do_remove_voter(&dv));
 
 			Ok(())