A one-time fast-growing regional airline is hitting turbulent times, like many of its much-larger rivals. ExpressJet Airlines, which started service from Sacramento International Airport a year ago, will eliminate service to Bakersfield, Oklahoma City and Tulsa, Okla., on Aug, 23. ExpressJet will also eliminate nonstop service from Sacramento to San Antonio.  The airline’s president said rising fuel costs and too much competition in some markets prompted the move to cut 30 percent of its flights schedule this fall. ExpressJet will drop from its current 13 flights daily from Sacramento to nine this fall, but the airline will add three nonstop flights to Ontario and introduce a once-a-day direct flight to Monterey. The airline serves 166 cities with about 1,450 flights daily.