Drop block field (yes, intentional) which GEO is not using

Bring in Block Class which is Drutopia standard (no these modules are not equivalent
at all they are just nearby alphabetically).

And upgrade Backup Migrate to 5 for Drupal 9 compatibility

Bringing our composer.json more in line with Drutopia Agaric-hosted
standard.

composer.json

@@ -32,8 +32,8 @@
         "cweagans/composer-patches": "^1.7",
         "drupal/allowed_formats": "^1.1",
         "drupal/antibot": "^1.2",
-        "drupal/backup_migrate": "^4.1",
-        "drupal/block_field": "^1.0@RC",
+        "drupal/backup_migrate": "^5",
+        "drupal/block_class": "^1.3",
         "drupal/ckeditorheight": "^1.3",
         "drupal/classitup": "^1.0@beta",
         "drupal/comment_notify": "dev-1.x",