remove unsed function

src/app.rs

@@ -44,20 +44,6 @@ pub struct CalendarApp {
     events: EventsCollection,
 }
 
-impl std::fmt::Display for ViewMode {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(
-            f,
-            "{}",
-            match self {
-                ViewMode::Week => "Week",
-                ViewMode::Month => "Month",
-                ViewMode::Year => "Year",
-            }
-        )
-    }
-}
-
 impl CalendarApp {
 	pub fn with_files(calendar_paths: std::vec::Vec<path::PathBuf>) -> Self {
         let view_date = Utc::now().date_naive();