remove unused re_convert prototype (fix #231)
remove unused re_convert prototype (fix #231)

kmaehashi/jubatus_core,kumagi/jubatus_core,gintenlabo/jubatus,rimms/jubatus_core,rimms/jubatus_core,gintenlabo/jubatus_core,kumagi/jubatus_core,kumagi/jubatus_core,jubatus/jubatus,kmaehashi/jubatus_core,mathn/jubatus,roselleebarle04/jubatus,rimms/jubatus,kmaehashi/jubatus_core,jubatus/jubatus,roselleebarle04/jubatus,gintenlabo/jubatus_core,gintenlabo/jubatus,kmaehashi/jubatus_core,kumagi/jubatus_core,Asuka52/jubatus,elkingtonmcb/jubatus,kmaehashi/jubatus,kmaehashi/jubatus,rimms/jubatus,gintenlabo/jubatus_core,jubatus/jubatus,rimms/jubatus_core,elkingtonmcb/jubatus,rimms/jubatus_core,Asuka52/jubatus,gintenlabo/jubatus_core,mathn/jubatus