reclass: opendaylight: Use UCA default repos

reclass: opendaylight: Use UCA default repos

Current opendaylight pillar enforces a full apt repository cleanup,
removing Ubuntu Cloud Archive (UCA) repos in favor of adding
pre-hardcoded Ubuntu archive repos.

Unlike UCA, main Ubuntu archive is split based on target arch, the
main archive.ubuntu.com holding only x86 packages, while the other
archs are hosted on ports.ubuntu.com.

This leads to adding (only) x86-specific repositories to our AArch64
UCA image.

Mitigate this by ommiting "system.linux.system.repo.ubuntu" from the
opendaylight pillar, leaving the default UCA repos in place.

Change-Id: Ia7033bcb544d8752d5557bbabc92c92c5008b00c
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>