core: layout: remove unreachable statement

This statement is the source of a warning because the statement above it
is already a catch-all. Remove it.

src/core/layout.rs

@@ -334,8 +334,6 @@ impl Part {
             KeyValue(Keysym::Delete, _) => false,
 
             KeyValue(_, l) => l != "",
-
-            _ => true,
         }
     }