I can't guarantee it will work with this specific file, but usually this works:

Open your workbook, and save it with different name (Save As). When you are lucky, the size of renamed workbook will be much less. An optional step will be to repeat the Save As, and overwrite the old workbook.

Why this works? Whenever anything is changed in Excel workbook (edited, added, deleted etc.), Excel keeps the history of those changes. Through the session, this history is used when user is restoring previous entries. After the file is closed, and then later opened again, any history from previous sessions is not accessible anymore, but it still remains there. When user saves the workbook with different name, the history of original workbook is cleared.

Edit. Just read about custom format - missed this at start. You may have entire worksheet formatted with this (Entire worksheet - not a range with data). When this is the case, deleting any number of rows/columns below/right of your datarange doesn't help - new rows/columns Excel adds after deleting are formatted too. To correct this, probably selecting entire worksheet, then removing all formats and saving the workbook, may help. Or you have to create a new sheet and transfer there all data, formulas, formats, etc. from datarange in old sheet (NB! Only from datarange!), and then delete the old one.