Hulu has axed the "Buffy the Vampire Slayer" reboot ... and we hear Sarah Michelle Gellar is quite disappointed with the shocking development. A source close to SMG and slated revival director Chloé Zhao tells TMZ … both women feel blindsided by the news, not to mention the timing -- as Sarah just had a killer opening at SXSW for her new movie "Ready or Not 2: Here I Come," and Chloe has the Oscars on Sunday for "Hamnet." We're told Sarah and Chloe were so looking forward to continuing Buffy’s