Ditch the input buffer (#2911)

* Pass input data via the scratch buffer.

Remove calls to ext_input_*.

* Fix tests and docs

* Bump the version.

* Remove ext_input_* from COMPLEXITY.md

* Return back the length check and add more comments

* Update the documentation of the scratch buffer.

* Fix a silly mistake.

substrate/srml/contracts/src/wasm/mod.rs

@@ -134,7 +134,7 @@ impl<'a, T: Trait> crate::exec::Vm<T> for WasmVm<'a, T> {
 
 		let mut runtime = Runtime::new(
 			ext,
-			input_data,
+			input_data.to_vec(),
 			empty_output_buf,
 			&self.schedule,
 			memory,