message: Remove obsolete failure case.
  We don't validate continuity in the BlockHeadersBatch::validate anymore.
  Continuity is validated in the Fetcher now.
diff: @@ -3213,27 +3213,6 @@ mod tests {
  )
  );
  - let reversed = {
  - let mut tmp = batch.inner().clone();
  - let correct_first = tmp.first().cloned().unwrap();
  - tmp.reverse();
  - // We are putting highest block at the first index of the batch.
  - // The rest of the batch is in ascending order.
  - // We do that b/c `BlockHeadersBatch::validate` first checks whether the highest header
  - // in the batch is the expected one and only later validates the continuity.
  - // We want to retain that validation order as checking the first header in the batch is
  - // faster than iterating over all headers.
  - if let Some(current_first) = tmp.first_mut() {
  - *current_first = correct_first
  - }
  - BlockHeadersBatch::new(tmp)
  - };
  -
  - assert_eq!(
  - Err(BlockHeadersBatchValidationError::BatchNotContinuous),
  - BlockHeadersBatch::validate(&reversed, &batch_id, &trusted, NEVER_SWITCH_HASHING)
  - );
  -
  let invalid_length_batch = BlockHeadersBatch::new(batch.inner().clone()[1..].to_vec());
  assert_eq!(
  