You can choose to hide columns in your custom report in the Custom Report Writer if you don't want it to show. You can even use this feature alongside calculated fields, so only the final calculated column will show in the report!
To hide a column in your report, edit your report and click the blue pencil icon next to the column name.
In the slide over, click the box next to Hide field to remove the column from your report without deleting it.
You can also manage whether columns are hidden or not in bulk. Just click the Bulk Edit Column Settings button.
In the slide over, click the boxes to remove the column from your report without deleting it. The columns you select will not be output in your report.