Auto merge of #8818 - koic:use_rust_2021_prelude, r=flip1995

Use the traits added to the Rust 2021 Edition prelude

Follow up rust-lang/rust#96861.

This PR uses the traits added to the Rust 2021 Edition prelude.

> The `TryInto`, `TryFrom` and `FromIterator` traits are now part of the prelude.

https://doc.rust-lang.org/edition-guide/rust-2021/prelude.html

Author: bors

clippy_lints/src/checked_conversions.rs

@@ -30,7 +30,6 @@ declare_clippy_lint! {
     /// Could be written:
     ///
     /// ```rust
-    /// # use std::convert::TryFrom;
     /// # let foo = 1;
     /// # let _ =
     /// i32::try_from(foo).is_ok()

clippy_lints/src/enum_clike.rs

@@ -8,7 +8,6 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, IntTy, UintTy};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
-use std::convert::TryFrom;
 
 declare_clippy_lint! {
     /// ### What it does

clippy_lints/src/excessive_bools.rs

@@ -4,8 +4,6 @@ use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{sym, Span};
 
-use std::convert::TryInto;
-
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for excessive

clippy_lints/src/fallible_impl_from.rs

@@ -32,7 +32,6 @@ declare_clippy_lint! {
     /// // Good
     /// struct Foo(i32);
     ///
-    /// use std::convert::TryFrom;
     /// impl TryFrom<String> for Foo {
     ///     type Error = ();
     ///     fn try_from(s: String) -> Result<Self, Self::Error> {

clippy_lints/src/index_refutable_slice.rs

@@ -14,7 +14,6 @@ use rustc_middle::ty;
 use rustc_semver::RustcVersion;
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{symbol::Ident, Span};
-use std::convert::TryInto;
 
 declare_clippy_lint! {
     /// ### What it does

clippy_lints/src/methods/mod.rs

@@ -1776,8 +1776,6 @@ declare_clippy_lint! {
     ///
     /// ### Example
     /// ```rust
-    /// use std::iter::FromIterator;
-    ///
     /// let five_fives = std::iter::repeat(5).take(5);
     ///
     /// let v = Vec::from_iter(five_fives);

clippy_lints/src/redundant_clone.rs

@@ -19,7 +19,6 @@ use rustc_mir_dataflow::{Analysis, AnalysisDomain, CallReturnPlaces, GenKill, Ge
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::{BytePos, Span};
 use rustc_span::sym;
-use std::convert::TryFrom;
 use std::ops::ControlFlow;
 
 macro_rules! unwrap_or_continue {

clippy_lints/src/regex.rs

@@ -7,7 +7,6 @@ use rustc_hir::{BorrowKind, Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::{BytePos, Span};
-use std::convert::TryFrom;
 
 declare_clippy_lint! {
     /// ### What it does

clippy_lints/src/tabs_in_doc_comments.rs

@@ -4,7 +4,6 @@ use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::{BytePos, Span};
-use std::convert::TryFrom;
 
 declare_clippy_lint! {
     /// ### What it does

clippy_utils/src/consts.rs

@@ -13,7 +13,6 @@ use rustc_middle::ty::{self, FloatTy, ScalarInt, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_span::symbol::Symbol;
 use std::cmp::Ordering::{self, Equal};
-use std::convert::TryInto;
 use std::hash::{Hash, Hasher};
 use std::iter;