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

crates/mdman/src/hbs.rs

@@ -7,7 +7,6 @@ use handlebars::{
     RenderContext, RenderError, Renderable,
 };
 use std::collections::HashMap;
-use std::convert::TryFrom;
 use std::path::Path;
 
 type FormatterRef<'a> = &'a (dyn Formatter + Send + Sync);

src/cargo/core/compiler/fingerprint.rs

@@ -313,7 +313,6 @@
 //! <https://github.com/rust-lang/cargo/issues?q=is%3Aissue+is%3Aopen+label%3AA-rebuild-detection>
 
 use std::collections::hash_map::{Entry, HashMap};
-use std::convert::TryInto;
 use std::env;
 use std::hash::{self, Hash, Hasher};
 use std::io;

src/cargo/sources/registry/index.rs

@@ -76,7 +76,6 @@ use cargo_util::{paths, registry::make_dep_path};
 use log::{debug, info};
 use semver::Version;
 use std::collections::{HashMap, HashSet};
-use std::convert::TryInto;
 use std::fs;
 use std::io::ErrorKind;
 use std::path::Path;

tests/testsuite/dep_info.rs

@@ -8,7 +8,6 @@ use cargo_test_support::{
     basic_bin_manifest, basic_manifest, is_nightly, main_file, project, rustc_host, Project,
 };
 use filetime::FileTime;
-use std::convert::TryInto;
 use std::fs;
 use std::path::Path;
 use std::str;