While getting rid of all the format(barebox_printf) warnings was nice,
it caused the printf calls in arch/sandbox/os/common.c to get directed
to the barebox versions rather than the libc ones causing a crash:

E.G. before this revert:
nm -a barebox|grep -w printf
0000000000404fa3 T print

And after:
nm -a barebox|grep -w printf
U printf@@GLIBC_2.2.5

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

This reverts commit 6b082cf.