feature_flags: Remove unused auto-watch flag (#62122)

Release Notes:

- N/A

crates/feature_flags/src/flags.rs

@@ -115,14 +115,6 @@ impl FeatureFlag for AgentThreadWorktreeLabelFlag {
 }
 register_feature_flag!(AgentThreadWorktreeLabelFlag);
 
-pub struct AutoWatchFeatureFlag;
-
-impl FeatureFlag for AutoWatchFeatureFlag {
-    const NAME: &'static str = "auto-watch-screens";
-    type Value = PresenceFlag;
-}
-register_feature_flag!(AutoWatchFeatureFlag);
-
 /// Wraps agent-run terminal commands in an OS-level sandbox where supported,
 /// and applies the shared per-host network grants to the `fetch` tool and the
 /// out-of-project write grants to the `create_directory` tool. When off,