Remove unused TUI collaboration mode indicators (#33872)

## What changed

Remove the unused `PairProgramming` and `Execute` footer indicator variants and their label and styling branches. Keep `Plan` as the only `CollaborationModeIndicator` rendered by the TUI.

GitOrigin-RevId: 5f3e6c8ff50a04d41dd5fc342cf1347a7e4f78fe

codex-rs/tui/src/bottom_pane/footer.rs

@@ -89,10 +89,6 @@ pub(crate) struct FooterProps {
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub(crate) enum CollaborationModeIndicator {
     Plan,
-    #[allow(dead_code)] // Hidden by current mode filtering; kept for future UI re-enablement.
-    PairProgramming,
-    #[allow(dead_code)] // Hidden by current mode filtering; kept for future UI re-enablement.
-    Execute,
 }
 
 #[derive(Clone, Debug, Eq, PartialEq)]
@@ -147,10 +143,6 @@ impl CollaborationModeIndicator {
         };
         match self {
             CollaborationModeIndicator::Plan => format!("Plan mode{suffix}"),
-            CollaborationModeIndicator::PairProgramming => {
-                format!("Pair Programming mode{suffix}")
-            }
-            CollaborationModeIndicator::Execute => format!("Execute mode{suffix}"),
         }
     }
 
@@ -158,8 +150,6 @@ impl CollaborationModeIndicator {
         let label = self.label(show_cycle_hint);
         match self {
             CollaborationModeIndicator::Plan => Span::from(label).magenta(),
-            CollaborationModeIndicator::PairProgramming => Span::from(label).cyan(),
-            CollaborationModeIndicator::Execute => Span::from(label).dim(),
         }
     }
 }