migrate_file 2.1.0

This release removes the old reuse and replace configuration options which are no longer supported in Drupal 9.x by the file_copy plugin (which our file_import plugin extends). The relevant core issue is #2877839: Reuse option in FileCopy migrate process plugin not work with remote files and the associated change record is at https://www.drupal.org/node/2981389

With these configuration options removed, we no longer support the 8.x branch of Drupal core (which is now unsupported anyway). Anyone still using migrate_file on Drupal 8.x will need to continue using the 2.0.x branch.