Use dependency injection

Problem/Motivation

The dependency injection could be implemented in TombstonesSettingsForm and TombstonesService classes.

Steps to reproduce

Check corresponding classes files, observe \Drupal::... calls.

Proposed resolution

Replace \Drupal::... calls with dependency injection.

Remaining tasks

Apply the fix.

User interface changes

None.

API changes

Any custom modules extending the tombstones.service service may have to be updated.

Data model changes

None.