ci-dockerfiles-sanity-check: Disable single-value matrix axis

It's unclear why it's being used, as originally this single-value
config was built on the same host as the parent job (build-amd64).
As we switch to build-amd64-private, just drop this axis at all.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I31f4053e9dad59cf64489a24a9f43801e7b3ed7d
1 file changed