fix(tui): drop a pinned-todos override committed without its implementation

c9ccb4f01 picked up an in-flight `pinned_todos_payload` override along with my
own change, but `pinned_todos_payload_ref` was never committed, so master could
not compile jcode-tui at all.

On master the override is dead code: its only consumer (the pinned todo band in
ui_viewport) is also uncommitted. Removing it restores the trait default, which
returns None, so nothing changes behaviourally and the build works again. The
feature can land intact with its implementation and consumer together.

Root cause was the same as 83d66905b: I assembled that commit by copying files
out of a scratch worktree, which swept up a neighbouring agent's partial work.
Targeted edits only from here.

crates/jcode-tui/src/tui/app/tui_state.rs

@@ -585,10 +585,6 @@ impl crate::tui::TuiState for App {
         &self.streaming.streaming_text
     }
 
-    fn pinned_todos_payload(&self) -> Option<&str> {
-        self.pinned_todos_payload_ref()
-    }
-
     fn input(&self) -> &str {
         &self.input
     }