NEWARK — It’s been more than 20 years since the state took the reins of Newark’s public school system, choosing its succession of superintendents and making decisions on staffing, instruction and budgeting. But next school year, the School Advisory Board is expected to shed its enfeebling title and become a fully-functioning board with the power to hire and fire its own chief of schools — governance of Newark’s 65 public schools will finally return to local control.