Eliminate PHP_CodeSniffer DrupalPractice warnings

$ phpcs --standard=DrupalPractice .

FILE: /var/www/html/drupal8/web/modules/contrib/forgot_username/src/Form/ForgotUsernameForm.php
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FOUND 0 ERRORS AND 10 WARNINGS AFFECTING 9 LINES
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 19 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 23 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 47 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 52 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 53 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 56 | WARNING | t() calls should be avoided in classes, use \Drupal\Core\StringTranslation\StringTranslationTrait and $this->t() instead
 64 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 64 | WARNING | Unused variable $language.
 65 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
 70 | WARNING | \Drupal calls should be avoided in classes, use dependency injection instead
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