Removed experimental "command risk assessment" feature (#7799)

This experimental feature received lukewarm reception during internal
testing. Removing from the code base.

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__approval_modal_exec.snap

@@ -2,6 +2,8 @@
 source: tui/src/chatwidget/tests.rs
 expression: terminal.backend().vt100().screen().contents()
 ---
+
+
   Would you like to run the following command?
 
   Reason: this is a test reason such as one that would be produced by the model

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__exec_approval_history_decision_approved_short.snap

@@ -3,4 +3,3 @@ source: tui/src/chatwidget/tests.rs
 expression: lines_to_single_string(&decision)
 ---
 ✔ You approved codex to run echo hello world this time
-