delete temporary travis enabled branch (#2956)
delete temporary travis enabled branch (#2956)

This branch was added during Python2 deprecation work and is no longer needed.
riga/luigi,dlstadther/luigi,jamesmcm/luigi,spotify/luigi,jamesmcm/luigi,spotify/luigi,dlstadther/luigi,riga/luigi,spotify/luigi,spotify/luigi,jamesmcm/luigi,jamesmcm/luigi,dlstadther/luigi,riga/luigi,dlstadther/luigi,riga/luigi