Clean up Main documents with attachment number 0

[albertisfu]

Once we stop merging documents with attachment 0, we should clean up Main documents with attachment_number 0 and set it to None.

For this, we can use the following query as a base:

RECAPDocument.objects.filter(
    document_type=RECAPDocument.PACER_DOCUMENT,
    document_number__isnull=False,
    attachment_number=0
)

We also have Main documents with attachment_number 1 (and probably other numbers), which we can review to determine if they need to be cleaned up as well.

RECAPDocument.objects.filter(
    document_type=RECAPDocument.PACER_DOCUMENT,
    document_number__isnull=False,
    attachment_number=1
)