The proviso of section 407(a) of the Civil Rights Act of 1964 [42 U.S.C. 2000c–6(a)] providing in substance that no court or official of the United States shall be empowered to issue any order seeking to achieve a racial balance in any school by requiring the transportation of pupils or students from one school to another or one school district to another in order to achieve such racial balance, or otherwise enlarge the existing power of the court to insure compliance with constitutional standards shall apply to all public school pupils and to every public school system, public school and public school board, as defined by title IV [42 U.S.C. 2000c