zone-size-limit: update test ixfr/transfer_size

tests-extra/tests/ixfr/transfer_size/data/example.com.zone

-$ORIGIN example.com.
-$TTL 3600
-
-@	SOA	dns1 hostmaster 2010111200 10800 3600 1209600 7200
-	NS	dns1
-
-dns1	A	192.0.2.1
-	A	192.0.2.2

tests-extra/tests/ixfr/transfer_size/data/example.com.zone.2

 $ORIGIN example.com.
 $TTL 3600
 
-@	SOA	dns1 hostmaster 2010111201 10800 3600 1209600 7200
+@	SOA	dns1 hostmaster 2010111202 10800 3600 1209600 7200
 	NS	dns1
 
 dns1	A	192.0.2.1

tests-extra/tests/ixfr/transfer_size/test.py

@@ -7,12 +7,10 @@ from dnstest.test import Test
 t = Test()
 
 master1 = t.server("knot")
-master2 = t.server("knot")
 slave = t.server("knot")
-zone = t.zone("example.com.", storage=".")
+zone = t.zone("example.com.", storage=".", version=1)
 slave.zone_size_limit = 230
 t.link(zone, master1, slave, ixfr=True)
-t.link(zone, master2, slave, ixfr=True)
 
 t.start()
 
@@ -28,11 +26,6 @@ master1.reload()
 master1.zone_wait(zone, serial)
 t.sleep(10)
 
-master2.update_zonefile(zone, version=1)  # smaller zone
-master2.reload()
-
-slave.zone_wait(zone, serial)
-
 resp = slave.dig("test.example.com.", "TXT")
 
 resp.check("passed")