Remove "SERIALNUM" define for Teensy 2
Remove "SERIALNUM" define for Teensy 2

jrobeson/platformio,valeros/platformio,jrobeson/platformio,bkudria/platformio,TimJay/platformio,bkudria/platformio,eiginn/platformio,TimJay/platformio,dkuku/platformio,mcanthony/platformio,platformio/platformio,bkudria/platformio,mseroczynski/platformio,platformio/platformio-core,platformio/platformio-core,TimJay/platformio,jrobeson/platformio,ZachMassia/platformio,atyenoria/platformio,jrobeson/platformio,awong1900/platformio,mplewis/platformio,awong1900/platformio,bkudria/platformio,awong1900/platformio,TimJay/platformio,TimJay/platformio