Fix #5299, disable shutdown header

I wanted to make this configurable, but passing that information via the backend, into React, into the client during hydration, started to touch lots of files. Hardcoding it keeps it simple.

server/src/promotion-strategy.js

@@ -74,7 +74,7 @@ class PromotionStrategy {
   }
 
   shouldShowDeprecation() {
-    return true;
+    return false;
   }
 }