bionic-amd64-tf-m-build: Remove unused ArmClang variables

Related for older ArmClang versions (pre-UBL) which were removed and no
longer supported.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I300282231ffa521e6674675eaf35aefb6e1da071
2 files changed