Don't take the origin in can_set_code (paritytech#6899)

It makes no sense that `can_set_code` takes the origin for checking it.
Everybody reusing this function is only interested in the other checks
that are done by this function. The origin should be checked by every
dispatchable individually.

frame/system/src/lib.rs

@@ -595,7 +595,8 @@ decl_module! {
 		/// # </weight>
 		#[weight = (T::MaximumBlockWeight::get(), DispatchClass::Operational)]
 		pub fn set_code(origin, code: Vec<u8>) {
-			Self::can_set_code(origin, &code)?;
+			ensure_root(origin)?;
+			Self::can_set_code(&code)?;
 
 			storage::unhashed::put_raw(well_known_keys::CODE, &code);
 			Self::deposit_event(RawEvent::CodeUpdated);
@@ -1234,14 +1235,10 @@ impl<T: Trait> Module<T> {
 
 	/// Determine whether or not it is possible to update the code.
 	///
-	/// This function has no side effects and is idempotent, but is fairly
-	/// heavy. It is automatically called by `set_code`; in most cases,
-	/// a direct call to `set_code` is preferable. It is useful to call
-	/// `can_set_code` when it is desirable to perform the appropriate
-	/// runtime checks without actually changing the code yet.
-	pub fn can_set_code(origin: T::Origin, code: &[u8]) -> Result<(), sp_runtime::DispatchError> {
-		ensure_root(origin)?;
-
+	/// Checks the given code if it is a valid runtime wasm blob by instantianting
+	/// it and extracting the runtime version of it. It checks that the runtime version
+	/// of the old and new runtime has the same spec name and that the spec version is increasing.
+	pub fn can_set_code(code: &[u8]) -> Result<(), sp_runtime::DispatchError> {
 		let current_version = T::Version::get();
 		let new_version = sp_io::misc::runtime_version(&code)
 			.and_then(|v| RuntimeVersion::decode(&mut &v[..]).ok())