Simple CSV combine and filter duplicates

I have two downloaded files, one is an hourly, one is an End Of Day for redundancy.

I need a BATCH SCRIPT to do the following:

1. Combine files "C:\LakesideBooksClient\Downloads\EbayOrdersDownload.csv" and "C:\LakesideBooksClient\Downloads\EbayOrdersDownloadEOD.csv"
2. Remove duplicate lines. Duplicate qualifier is column "lineItemID".
3. Save/overwrite edited file as "C:\LakesideBooksClient\Downloads\EbayOrdersDownload.csv"
4. Delete "C:\LakesideBooksClient\Downloads\EbayOrdersDownloadEOD.csv"
5. Close cmd

File Location = C:\LakesideBooksClient\Downloads (obviously)

Name Script "EbayOrdersGetCombine".bat