docs: cleanup inner region tags (#764)

* docs: standardizing region tags to be consistent with other related snippets * docs: cleanup old tags now that new ones are live

Author: Anthony

samples/snippets/src/main/java/com/example/spanner/SpannerSample.java

@@ -1623,7 +1623,6 @@ static void createBackup(
  // [END spanner_create_backup]
 
  // [START spanner_cancel_backup_create]
- // [START spanner_cancel_create_backup]
  static void cancelCreateBackup(
  DatabaseAdminClient dbAdminClient, DatabaseId databaseId, BackupId backupId) {
  // Set expire time to 14 days from now.
@@ -1666,7 +1665,6 @@ static void cancelCreateBackup(
  throw SpannerExceptionFactory.propagateInterrupt(e);
  }
  }
- // [END spanner_cancel_create_backup]
  // [END spanner_cancel_backup_create]
 
  // [START spanner_list_backup_operations]