Patch to remove duplicate entries created due to change in

validation_logic in Table Mapper Detail for the following doctypes:
* Delivery Note-Receivable Voucher
* Purchase Order-Purchase Voucher
* Sales Order-Receivable Voucher

erpnext/patches/remove_duplicate_table_mapper_detail.py

@@ -0,0 +1,22 @@
+"""
+	Removes duplicate entries created in 
+"""
+import webnotes
+def execute():
+	res = webnotes.conn.sql("""\
+		SELECT a.name
+		FROM
+			`tabTable Mapper Detail` a,
+			`tabTable Mapper Detail` b
+		WHERE
+			a.parent = b.parent AND
+			a.from_table = b.from_table AND
+			a.to_table = b.to_table AND
+			a.from_field = b.from_field AND
+			a.to_field = b.to_field AND
+			a.name < b.name""")
+	if res and len(res)>0:
+		name_string = ", ".join(["'" + str(r[0]) + "'" for r in res])
+		res = webnotes.conn.sql("""\
+			DELETE FROM `tabTable Mapper Detail`
+			WHERE name IN (%s)""" % name_string)