yoda: warning cleanup sweep (dead code + clippy --fix) (squashed)

Squash of 4 yoda commits:
- 84437e21 yoda: libcosmic-yoda dead-code purge (14->0 warnings)
- 999db0a4 yoda: cosmic-theme cleanup (4->0 warnings) — workspace at 0 warnings total
- 4743bb8e yoda: cargo clippy --fix on libcosmic-yoda (115->33 warnings)
- 675f3b59 chore: reduce local stack warnings

src/desktop.rs

@@ -769,7 +769,7 @@ impl DesktopEntryData {
 pub async fn spawn_desktop_exec<S, I, K, V>(
     exec: S,
     env_vars: I,
-    app_id: Option<&str>,
+    _app_id: Option<&str>,
     terminal: bool,
 ) where
     S: AsRef<str>,
@@ -816,13 +816,17 @@ pub async fn spawn_desktop_exec<S, I, K, V>(
     // https://systemd.io/DESKTOP_ENVIRONMENTS
     //
     // Similar to what Gnome sets, for now.
-    if let Some(pid) = crate::process::spawn(cmd).await {
+    if let Some(_pid) = crate::process::spawn(cmd).await {
         #[cfg(feature = "desktop-systemd-scope")]
         if let Ok(session) = zbus::Connection::session().await {
             if let Ok(systemd_manager) = SystemdMangerProxy::new(&session).await {
                 let _ = systemd_manager
                     .start_transient_unit(
-                        &format!("app-cosmic-{}-{}.scope", app_id.unwrap_or(&executable), pid),
+                        &format!(
+                            "app-cosmic-{}-{}.scope",
+                            _app_id.unwrap_or(&executable),
+                            _pid
+                        ),
                         "fail",
                         &[
                             (
@@ -833,7 +837,7 @@ pub async fn spawn_desktop_exec<S, I, K, V>(
                             ),
                             (
                                 "PIDs".to_string(),
-                                zbus::zvariant::Value::from(vec![pid])
+                                zbus::zvariant::Value::from(vec![_pid])
                                     .try_to_owned()
                                     .unwrap(),
                             ),