Fix Dependency Injection problems in the module

Problem/Motivation

FILE: src/Form/EntityDeleteConfirmationForm.php
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FOUND 0 ERRORS AND 6 WARNINGS AFFECTING 6 LINES
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  46 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  60 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  74 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
  92 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 128 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
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FILE: src/Form/EntityDeleteForm.php
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FOUND 0 ERRORS AND 5 WARNINGS AFFECTING 5 LINES
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 114 | WARNING |  \Drupal calls should be avoided in classes, use dependency injection instead
 137 | WARNING |  \Drupal calls should be avoided in classes, use dependency injection instead
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Time: 147ms; Memory: 10MB

Steps to reproduce

Run phpcs. There's also other problems, but lets fix them in a separated issue.

Proposed resolution

Fix them all

Remaining tasks

User interface changes

API changes

Data model changes