refactor: remove unused default_meta_plugin_type function

Co-authored-by: aider (openai/andrew.openrouter.qwen.qwen3-coder) <aider@aider.chat>

src/meta_plugin.rs

@@ -78,8 +78,3 @@ pub fn get_meta_plugin(meta_plugin_type: MetaPluginType) -> Box<dyn MetaPlugin>
     }
 }
 
-pub fn default_meta_plugin_type() -> MetaPluginType {
-    // Default meta plugin functionality has been removed
-    // This function returns a placeholder value
-    MetaPluginType::FileMagic
-}