heteroprio: simplify code by using starpu's functions and correct mistakes

3 jobs for !27 with update/auto-heteroprio in 19 minutes and 43 seconds (queued for 3 seconds)
latest detached
Status Job ID Name Coverage
  Build
passed #1226938
build

00:05:38

 
  Deploy
passed #1226939
check

00:10:15

passed #1226940
simgrid

00:03:49