Remove useless imports (#11136)

Because `TryInto`/`TryFrom` are in prelude by default from edition 2021

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

substrate/frame/election-provider-support/src/mock.rs

@@ -21,7 +21,6 @@
 
 use std::{
 	collections::{HashMap, HashSet},
-	convert::TryInto,
 	hash::Hash,
 };
 

substrate/frame/election-provider-support/src/tests.rs

@@ -22,7 +22,6 @@
 use crate::{mock::*, IndexAssignment, NposSolution};
 use frame_support::traits::ConstU32;
 use rand::SeedableRng;
-use std::convert::TryInto;
 
 mod solution_type {
 	use super::*;
@@ -30,7 +29,7 @@ mod solution_type {
 	// these need to come from the same dev-dependency `frame-election-provider-support`, not from
 	// the crate.
 	use crate::{generate_solution_type, Assignment, Error as NposError, NposSolution};
-	use sp_std::{convert::TryInto, fmt::Debug};
+	use sp_std::fmt::Debug;
 
 	#[allow(dead_code)]
 	mod __private {

substrate/frame/election-provider-support/src/traits.rs

@@ -22,16 +22,12 @@ use codec::Encode;
 use scale_info::TypeInfo;
 use sp_arithmetic::traits::{Bounded, UniqueSaturatedInto};
 use sp_npos_elections::{ElectionScore, Error, EvaluateSupport};
-use sp_std::{
-	convert::{TryFrom, TryInto},
-	fmt::Debug,
-	prelude::*,
-};
+use sp_std::{fmt::Debug, prelude::*};
 
 /// An opaque index-based, NPoS solution type.
 pub trait NposSolution
 where
-	Self: Sized + for<'a> sp_std::convert::TryFrom<&'a [IndexAssignmentOf<Self>], Error = Error>,
+	Self: Sized + for<'a> TryFrom<&'a [IndexAssignmentOf<Self>], Error = Error>,
 {
 	/// The maximum number of votes that are allowed.
 	const LIMIT: usize;