Revert "Correctly fetch batch regions in fuzz task (#4569)"

This reverts commit 8d7b9ab.

src/clusterfuzz/_internal/cron/schedule_fuzz.py

@@ -182,15 +182,8 @@ def get_fuzz_tasks(available_cpus: int) -> [tasks.Task]:
 
 
 def get_batch_regions(batch_config):
-  fuzz_subconf_names = {
-      subconf['name'] for subconf in batch_config.get(
-          'mapping.LINUX-PREEMPTIBLE-UNPRIVILEGED.subconfigs')
-  }
-  subconfs = batch_config.get('subconfigs')
-  return list(
-      set(subconfs[subconf]['region']
-          for subconf in subconfs
-          if subconf in fuzz_subconf_names))
+  mapping = batch_config.get('mapping')
+  return list(set(config['gce_region'] for config in mapping.values()))
 
 
 def schedule_fuzz_tasks() -> bool: