Delete compiler flags after removing Library Model

Remove the unnecessary compiler flags after deprecating the
Library Model in TF-M (no separate veneers will be generated
for the secure functions of a partition).

The associated modification in TF-M:
d23bbb336820ce0f651a101233cb2cea704b3393

Change-Id: Ib9c9c394b7d45e657d07c50d970e5f0e82528264
Signed-off-by: David Vincze <david.vincze@arm.com>
4 files changed