removed use of connection serial from the code

ably/realtime_conn.go

@@ -61,10 +61,6 @@ type Connection struct {
 	// a realtime client docs for more info (RTN9).
 	key string
 
-	// serial is the serial number of the last message to be received on this connection, used automatically by
-	// the library when recovering or resuming a connection. When recovering a connection explicitly, the recoveryKey
-	// is used in the recover client options as it contains both the key and the last message serial (RTN10).
-	serial       *int64
 	msgSerial    int64
 	connStateTTL durationFromMsecs
 	err          error
@@ -523,14 +519,6 @@ func (c *Connection) CreateRecoveryKey() string {
 	return recoveryKey
 }
 
-// Serial gives serial number of a message received most recently.
-// Last known serial number is used when recovering connection state.
-func (c *Connection) Serial() *int64 {
-	c.mtx.Lock()
-	defer c.mtx.Unlock()
-	return c.serial
-}
-
 // State returns current state of the connection.
 func (c *Connection) State() ConnectionState {
 	c.mtx.Lock()

ably/realtime_conn_integration_test.go

@@ -57,11 +57,6 @@ func TestRealtimeConn_NoConnect(t *testing.T) {
 	err := ablytest.Wait(ablytest.ConnWaiter(client, client.Connect, ably.ConnectionEventConnected), nil)
 	assert.NoError(t, err, "Connect()=%v", err)
 
-	serial := client.Connection.Serial()
-	assert.NotNil(t, serial)
-	assert.Equal(t, int64(-1), *serial,
-		"want serial=-1; got %d", client.Connection.Serial())
-
 	err = ablytest.FullRealtimeCloser(client).Close()
 	assert.NoError(t, err,
 		"ablytest.FullRealtimeCloser(client).Close()=%v", err)

ably/realtime_conn_spec_integration_test.go

@@ -2034,11 +2034,6 @@ func TestRealtimeConn_RTN16(t *testing.T) {
 			reason := client2.Connection.ErrorReason()
 			assert.Equal(t, 80008, int(reason.Code),
 				"expected 80008 got %d", reason.Code)
-			serial := client2.Connection.Serial()
-			assert.NotNil(t, serial)
-			// verify serial is -1 (new connection), not 5
-			assert.Equal(t, int64(-1), *serial,
-				"expected -1 got %d", serial)
 			msgSerial := client2.Connection.MsgSerial()
 			// verify msgSerial is 0 (new connection), not 3
 			assert.Equal(t, int64(0), msgSerial,