bionic-amd64-tf-a-build: Remove unused image

We fully migrated to jammy-amd64-tf-a-build image some time ago. Remove
this old image to not have stale unmaintained content in the repo.

(Specific cause for removal is switchover to UBL-enabled ArmClang version.
We don't want to upgrade this image as it's unused, and it's confusing to
have it around with no longer supported ArmClang versions referenced).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Ibfd7edee3b9a2a182c9879e1e088187c5cdeb288
6 files changed