cml1: remove needless check for write_taint attribute

cml1: remove needless check for write_taint attribute

The 'FIXME' comment itself says to remove this once the minimum bitbake
version has been bumped. This was in 2012.

The function was introduced in bitbake commit f7b55a94 ("bitbake:
bitbake: ensure -f causes dependent tasks to be re-run") and is already
part of bitbake 1.15.3 which is the minimum bitbake version since
'danny'.

Remove the check.

Signed-off-by: Enrico Jörns <ejo@pengutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>