Replace user module PrivateTempStore with core PrivateTempStore

@T-lo
Thanks for working on this. It appears that it needs more work than just changing the use statements though. Without having looked at where in the code this private temp store is used, I say that it's likely that a different service needs to be passed around.

Fixed the dependency injection in \Drupal\feeds\Plugin\Action\DeleteFeed

I get an error when trying to delete a feed when using the action "Delete selected feeds" on admin/content/feed.

This is because DeleteMultiple::create() still passes the service 'user.private_tempstore'. It would be cool if we had test coverage for this action.

The website encountered an unexpected error. Please try again later.
TypeError: Argument 1 passed to Drupal\feeds\Form\DeleteMultiple::__construct() must be an instance of Drupal\Core\PrivateTempStoreFactory, instance of Drupal\user\PrivateTempStoreFactory given, called in /Websites/drupal/drupalsites/drupal8/modules/wip/feeds8/feeds/src/Form/DeleteMultiple.php on line 71 in Drupal\feeds\Form\DeleteMultiple->__construct() (line 58 of modules/wip/feeds8/feeds/src/Form/DeleteMultiple.php).

Drupal\feeds\Form\DeleteMultiple->__construct(Object, Object, Object) (Line: 71)
Drupal\feeds\Form\DeleteMultiple::create(Object) (Line: 28)
Drupal\Core\DependencyInjection\ClassResolver->getInstanceFromDefinition('Drupal\feeds\Form\DeleteMultiple') (Line: 48)
Drupal\Core\Controller\HtmlFormController->getFormObject(Object, 'Drupal\feeds\Form\DeleteMultiple') (Line: 78)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 582)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 665)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Opened #3030879: Add test coverage for "feeds_feed_delete_action" for adding test coverage for the action "Delete selected feeds".

Alright, test coverage has now catched the bug introduced by the patch in #7.

New patch to fix that bug.

Correcting namespaces.

Committed #12.