Fix warnings after latest rust upgrade (#33043)

This fixes various unused code warnings after the recent rust upgrade.
Some of the dead code is maintained, as it is quite likely that it will
be used in future changes.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/devtools/actors/object.rs

@@ -11,7 +11,7 @@ use crate::StreamId;
 
 pub struct ObjectActor {
     pub name: String,
-    pub uuid: String,
+    pub _uuid: String,
 }
 
 impl Actor for ObjectActor {
@@ -37,7 +37,7 @@ impl ObjectActor {
             let name = registry.new_name("object");
             let actor = ObjectActor {
                 name: name.clone(),
-                uuid: uuid.clone(),
+                _uuid: uuid.clone(),
             };
 
             registry.register_script_actor(uuid, name.clone());