What does Primo Levi means when he says, "It was my good fortunate to be deported to Auschwitz in only 1944"?

Auschwitz was in operation during the years of 1940–1945, and, as the war progressed in Europe, the Nazi regime changed, and their treatment of prisoners changed. For starters, as the camp closed down and released its prisoners in the middle of 1945, being sent there in 1944 meant you had a year or possibly less to stay in Auschwitz. Obviously this is much better than being sent there in 1940 and trying to survive for 5 or more years in its cruel treatment and risking being sent to the gas chamber.
Additionally, as the war went along, soldiers were drawn away from the camps to active duty more often, so the number of guards to observe and punish prisoners became depleted, and the camp became less organized as time went on. Because of this, while it was still a tormenting place, prisoners were punished slightly less often and less severely and in many cases were less likely to be sent to the gas chamber than earlier on in the war.

As Levi goes on to explain after making the statement about his good fortune, he was lucky to arrive at Auschwitz in 1944 and not earlier because, by 1944, the Germans had decided to treat the Auschwitz prisoners slightly more humanely than they had before.
It was late in World War II, and Germany was losing—with heavy casualties. Therefore, the country was short on the manpower in the concentration camps that helped supply the war machine. The Germans decided to improve conditions so that prisoners would survive longer, in order to get more work out of them before they were eventually killed. For example, food rations were increased so that the prisoners would not starve so quickly. Further, guards were restrained from killing individual prisoners. These factors increased Levi's chances for survival in a brutal environment.
Nevertheless, the conditions Levi describes are horrible, so to some extent Levi's statement is ironic. Of course, it was anything but "good fortune" to end up in a Nazi concentration camp; the fact that conditions were not as absolutely horrible as they could have been was just the slimmest of good luck in a terrible situation.