HOLLYWOOD, June 23, 2000 -- If we can call Fox's "Titan A.E." a bomb (and since the $80 million toon only made $9.3 million last weekend, let's do just that), then did its shrapnel take out a studio chief? Officially, Fox Chairman Bill Mechanic resigned Thursday to launch his own film company. Unofficially, the word is that Fox honchos were none too happy with Mechanic's recent string of un-hits: "Fight Club," "Anna and the King" and the aforementioned "Titan A.E." Of course, Mechanic is also bailing before Fox opens one of its seemingly can't-miss properties: "Me, Myself & Irene" with Jim Carrey. "The studio is in excellent shape with a strong summer lineup and terrific product into next summer," Mechanic said in a statement, "and so I feel now is the time to pursue other personal ambitions." No time like the present -- and before another potentially troublesome