There might be more than one root=/dev/foo in the config file which
would cause unepected errros on the installed target, so remove all of
them.
[YOCTO #9354]
(From OE-Core rev: ca402bc3bc4e9a5c3e19a6ca504017335212b2c9)
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>