Replace deprecated usage of Drupal::entityManager with a Drupal::entityTypeManager

Problem/Motivation

Drupal:entityManager is deprecated and need to be replaced. Read more at: https://www.drupal.org/node/2549139

Proposed resolution

Replace the Drupal:entityManager by Drupal::entityTypeManager

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.