util: purge all code for testing OOM handling

util: purge all code for testing OOM handling

The OOM handling requires special build time options which we never
enable in our CI. Even once enabled the tests are incredibly slow and
typically require manual inspection of the results to weed out false
positives.

Since there was previous agreement to switch to abort on OOM in libvirt
code, there's no point continuing to keep the unused OOM testing code.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>