settings: Use a derive macro for refine (#38451)

When we refactored settings to not pass JSON blobs around, we ended up
needing
to write *a lot* of code that just merged things (like json merge used
to do).

Use a derive macro to prevent typos in this logic.

Release Notes:

- N/A

crates/call/src/call_settings.rs

@@ -1,6 +1,5 @@
 use gpui::App;
 use settings::Settings;
-use util::MergeFrom;
 
 #[derive(Debug)]
 pub struct CallSettings {
@@ -9,7 +8,7 @@ pub struct CallSettings {
 }
 
 impl Settings for CallSettings {
-    fn from_defaults(content: &settings::SettingsContent, _cx: &mut App) -> Self {
+    fn from_settings(content: &settings::SettingsContent, _cx: &mut App) -> Self {
         let call = content.calls.clone().unwrap();
         CallSettings {
             mute_on_join: call.mute_on_join.unwrap(),
@@ -17,13 +16,6 @@ impl Settings for CallSettings {
         }
     }
 
-    fn refine(&mut self, content: &settings::SettingsContent, _cx: &mut App) {
-        if let Some(call) = content.calls.clone() {
-            self.mute_on_join.merge_from(&call.mute_on_join);
-            self.share_on_join.merge_from(&call.share_on_join);
-        }
-    }
-
     fn import_from_vscode(
         _vscode: &settings::VsCodeSettings,
         _current: &mut settings::SettingsContent,