7 files declare their use of BookManagerInterface in Drupal 8

BookAdminEditForm.php in core/modules/book/src/Form/BookAdminEditForm.php

BookController.php in core/modules/book/src/Controller/BookController.php

BookNavigationBlock.php in core/modules/book/src/Plugin/Block/BookNavigationBlock.php

BookNodeIsRemovableAccessCheck.php in core/modules/book/src/Access/BookNodeIsRemovableAccessCheck.php

BookOutlineConstraintValidator.php in core/modules/book/src/Plugin/Validation/Constraint/BookOutlineConstraintValidator.php

BookOutlineForm.php in core/modules/book/src/Form/BookOutlineForm.php

BookRemoveForm.php in core/modules/book/src/Form/BookRemoveForm.php