Hi,

then you can have after insert BR on sc_req_item table

Condition: current.cat_item.name == 'Your Item Name'

Script:

if(current.variables.attachmentVariable == ''){
	var gr = new GlideRecord("sys_attachment");
	gr.addQuery("table_sys_id", current.getUniqueValue());
	gr.query();
	if (gr.next()) {
		gr.deleteRecord();
	}
}

Regards
Ankur