Use AOKP/system...

<project path="system/core" name="AOKP/system_core" remote="aokp" revision="jb-mr1" />
  <project path="system/extras" name="AOKP/system_extras" remote="aokp" revision="jb-mr1" />
  <project path="system/vold" name="AOKP/system_vold" remote="aokp" revision="jb-mr1" />