Remove old flags.

RELNOTES:
 Removed flags `--incompatible_checked_arithmetic`, `--incompatible_dict_literal_has_no_duplicates`, `--incompatible_disallow_keyword_only_args`, and ` --incompatible_comprehension_variables_do_not_leak`.
PiperOrigin-RevId: 185977740
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
index 38a4781..f7aba2c 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/ValidationEnvironment.java
@@ -143,13 +143,9 @@
 
   @Override
   public void visit(AbstractComprehension node) {
-    if (semantics.incompatibleComprehensionVariablesDoNotLeak()) {
-      openBlock();
-      super.visit(node);
-      closeBlock();
-    } else {
-      super.visit(node);
-    }
+    openBlock();
+    super.visit(node);
+    closeBlock();
   }
 
   @Override