Replace CollectVariables with locals(), update callsites to walk locals instead

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 5142817986cc56dd7057f548ab04bffa73ff4f2b..551062a8718d53eef420810233e380f71c299302 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -4003,9 +4003,7 @@ Genesis::Genesis(Isolate* isolate,
 
   // Check that the script context table is empty except for the 'this' binding.
   // We do not need script contexts for native scripts.
-  if (!FLAG_global_var_shortcuts) {
-    DCHECK_EQ(1, native_context()->script_context_table()->used());
-  }
+  DCHECK_EQ(1, native_context()->script_context_table()->used());
 
   result_ = native_context();
 }