Delete key files based on declaration by test cases and
not based on a hardcoded list of identifiers as in
test_suite_psa_crypto_slot_management.function. This fixes
the fact that in case of error the file associated to the
key identifier PSA_KEY_ID_VENDOR_MAX was not purged
(register_key_smoke_test test function).
Signed-off-by: Ronald Cron <ronald.cron@arm.com>