udev: drop dependency on udev in libudev

udev: drop dependency on udev in libudev

libudev previously depended on udev, but this causes problems with multilib
if the user wants to install two variants of libudev as they'll pull in two
variants of udev, which will conflict.

Instead, remove the dependency and rely that the image pulls in udev in some
way, such as the commonly used packagegroup-core-boot.

(From OE-Core rev: 6168ea4e00fd1c8296fe770fa9e2ef00018f5621)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>