Revert "fix: Concurrency issues in Sales and Purchase returns" (#34202)

Revert "fix: Concurrency issues in Sales and Purchase returns (#34019)"

This reverts commit a67284e96d.

(cherry picked from commit e26c6dc76b)

erpnext/controllers/sales_and_purchase_return.py

@@ -252,7 +252,6 @@ def get_already_returned_items(doc):
 			child.parent = par.name and par.docstatus = 1
 			and par.is_return = 1 and par.return_against = %s
 		group by item_code
-		for update
 	""".format(
 			column, doc.doctype, doc.doctype
 		),