Fix the issues reported by phpcs

Hello,

I have fixed PHPCS errors and warnings. Please review MR.

Thank you!

Applied MR !3. There are some more issues needs to be fixed.

./vendor/bin/phpcs --standard=Drupal,DrupalPractice --extensions=php,module,inc,install,test,profile,theme,css,info,txt,md,yml,twig,js,scss domain_registration 

FILE: ...ax domain_registration/domain_registration.info.yml
--------------------------------------------------------------------------------
FOUND 0 ERRORS AND 3 WARNINGS AFFECTING 1 LINE
--------------------------------------------------------------------------------
 1 | WARNING | Remove "project" from the info file, it will be added by
   |         | drupal.org packaging automatically
 1 | WARNING | Remove "datestamp" from the info file, it will be added by
   |         | drupal.org packaging automatically
 1 | WARNING | Remove "version" from the info file, it will be added by
   |         | drupal.org packaging automatically
--------------------------------------------------------------------------------


FILE: ... domain_registration/domain_registration.module
--------------------------------------------------------------------------------
FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
--------------------------------------------------------------------------------
 8 | WARNING | Global constants should not be used, move it to a class or
   |         | interface
 9 | WARNING | Global constants should not be used, move it to a class or
   |         | interface
--------------------------------------------------------------------------------


FILE: ... domain_registration/src/Tests/DomainRegistrationTest.php
--------------------------------------------------------------------------------
FOUND 0 ERRORS AND 16 WARNINGS AFFECTING 16 LINES
--------------------------------------------------------------------------------
  35 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  36 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  53 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  54 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  71 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  72 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  89 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
  90 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 107 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 108 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 125 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 126 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 144 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 145 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 162 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
 163 | WARNING | t() calls should be avoided in classes, use
     |         | \Drupal\Core\StringTranslation\StringTranslationTrait and
     |         | $this->t() instead
--------------------------------------------------------------------------------

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