don't fetch_tarballs twice
don't fetch_tarballs twice

fetch_tarballs is called by bootstrap when DO_FETCH_EXTERNAL is set to
true. So calling this here another time does not yield any benefit.

You could see this was happening, because it checked for wget and
mdsum twice at the beginning of each build.

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core