put TryInto and TryFrom in sp_std::prelude (#10183)

* Switch to Rust 2021

* Update trybuild to fix errors

* half baked

* fix

* remove unused import

* remove more warnings

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

substrate/frame/benchmarking/src/analysis.rs

@@ -18,7 +18,6 @@
 //! Tools for analyzing the benchmark results.
 
 use crate::BenchmarkResult;
-use core::convert::TryFrom;
 use linregress::{FormulaRegressionBuilder, RegressionDataBuilder};
 use std::collections::BTreeMap;