opkg-utils: don't generate PN-dev and PN-staticdev
opkg-utils ends up in any opkg/rpm image with package management as it's the
provider for update-alternatives. If dev-pkgs is enabled then opkg-utils-dev
will get installed, which is empty but will subsequently pull python3-dev into
the image (as opkg-utils-python depends on python3).
As this can result in all of Python appearing in otherwise small images, don't
generate these pointless packages.
Signed-off-by: Ross Burton <ross.burton@intel.com>
