Discard Executor (paritytech#1855)

closes paritytech#622 

Pros:
* simpler interface, just functions:
`create_runtime_from_artifact_bytes()` and `execute_artifact()`

Cons:
* extra overhead of constructing executor semantics each time

I could make it a combination of
* `create_runtime_config(params)` (such that we could clone the
constructed semantics)
* `create_runtime(blob, config)`
* `execute_artifact(blob, config, params)`

Not sure if it's worth it though.

---------

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

substrate/frame/support/procedural/src/pallet/expand/warnings.rs

@@ -33,6 +33,7 @@ pub(crate) fn weight_witness_warning(
  if dev_mode {
  return
  }
+
  let CallWeightDef::Immediate(w) = &method.weight else { return };
 
  let partial_warning = Warning::new_deprecated("UncheckedWeightWitness")
@@ -64,6 +65,7 @@ pub(crate) fn weight_constant_warning(
  if dev_mode {
  return
  }
+
  let syn::Expr::Lit(lit) = weight else { return };
 
  let warning = Warning::new_deprecated("ConstantWeight")