Client not deleting SQS messages

Currently, the delete_messages function fails to delete the message in SQS because it is unable to get the correct original receipt handle. It's a simple fix.

```python
def _get_original_receipt_handle(self, modified_receipt_handle: str) -> str:
"""
Responsible for returning the receipt handle of the message before
it was modified.

:modified_receipt_handle: Represents the receipt handle which was modified
when the message was stored in S3.

"""
return modified_receipt_handle.split(S3_KEY_MARKER)[-1]
```