Update to edition 2021

Remove unnecessary imports now included in prelude

Signed-off-by: mulhern <amulhern@redhat.com>

Cargo.toml

@@ -9,7 +9,7 @@ readme = "README.md"
 categories = ["os::linux-apis", "api-bindings"]
 keywords = ["Linux", "device", "mapper", "libdm", "storage"]
 license = "MPL-2.0"
-edition = "2018"
+edition = "2021"
 exclude = [".clippy.toml", ".githooks/*", ".gitignore", ".github/*", "Makefile"]
 
 [dependencies]

src/core/deviceinfo.rs

@@ -2,8 +2,6 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-use std::convert::TryFrom;
-
 use nix::libc::c_char;
 use semver::Version;
 

src/core/dm.rs

@@ -4,7 +4,6 @@
 
 use std::{
     cmp,
-    convert::TryInto,
     fs::File,
     io::{Cursor, Read, Write},
     mem::size_of,

src/testing/loopbacked.rs

@@ -3,7 +3,6 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 use std::{
-    convert::TryInto,
     fs::OpenOptions,
     io::{self, Seek, SeekFrom, Write},
     os::unix::io::AsRawFd,