Clippy updates

These are minor lint improvements suggested by current clippy.

src/cli/download_tracker.rs

@@ -155,7 +155,7 @@ impl DownloadTracker {
     fn display(&mut self) {
         match self.start_sec {
             // Maybe forgot to call `prepare_for_new_download` first
-            None => return,
+            None => {}
             Some(start_sec) => {
                 // Panic if someone pops the default bytes unit...
                 let unit = *self.units.last().unwrap();

src/cli/setup_mode.rs

@@ -106,7 +106,7 @@ pub fn main() -> Result<()> {
 
     let opts = InstallOpts {
         default_host_triple: default_host,
-        default_toolchain: default_toolchain.to_owned(),
+        default_toolchain,
         profile: profile.to_owned(),
         no_modify_path,
         components: &components,

src/dist/dist.rs

@@ -332,8 +332,7 @@ impl FromStr for PartialToolchainDesc {
     type Err = Error;
     fn from_str(name: &str) -> Result<Self> {
         let parsed: ParsedToolchainDesc = name.parse()?;
-        let target =
-            PartialTargetTriple::new(parsed.target.as_ref().map(|c| c.as_str()).unwrap_or(""));
+        let target = PartialTargetTriple::new(parsed.target.as_deref().unwrap_or(""));
 
         target
             .map(|target| Self {