Revert "setools: fix race condition"

This reverts commit 1ac68fe2.

Further investigations revealed that the problem wasn't a race condition
but the lack of flex package in the host machine:

  https://github.com/TresysTechnology/setools3/issues/5#issuecomment-144048612



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>