Erase ComponentDescriptorRegistry before inserting it to fix crash

Summary:
Changelog: [internal]

if you called `ContextContainer.insert("key", <value>)` and then again `ContextContainer.insert("key", <new_value>)`, the old value will remain in `ContextContainer`. This seems to be by design however it causes crash when reloading surface that uses `ComponentDescriptorRegistry_DO_NOT_USE_PRETTY_PLEASE`.

We fix it by erasing `ComponentDescriptorRegistry_DO_NOT_USE_PRETTY_PLEASE` in Scheduler before inserting a new one.

Reviewed By: shergin

Differential Revision: D18421153

fbshipit-source-id: a01e5f6ac864fd641674d84e97d447f8cb9114be

ReactCommon/fabric/uimanager/Scheduler.cpp

@@ -72,8 +72,11 @@ Scheduler::Scheduler(
     uiManagerBinding->attach(uiManager);
   });
 
+  auto componentDescriptorRegistryKey =
+      "ComponentDescriptorRegistry_DO_NOT_USE_PRETTY_PLEASE";
+  schedulerToolbox.contextContainer->erase(componentDescriptorRegistryKey);
   schedulerToolbox.contextContainer->insert(
-      "ComponentDescriptorRegistry_DO_NOT_USE_PRETTY_PLEASE",
+      componentDescriptorRegistryKey,
       std::weak_ptr<ComponentDescriptorRegistry const>(
           componentDescriptorRegistry_));