Remove config.py call on now-internal option

It turns out config.py wouldn't complain, but it's still confusing.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 0758282..7c89e7f 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2354,7 +2354,6 @@
     # Also unset MD_C and things that depend on it.
     if [ "$DRIVER_ONLY" -eq 1 ]; then
         scripts/config.py unset MBEDTLS_MD_C
-        scripts/config.py unset MBEDTLS_MD_LIGHT
     fi
     scripts/config.py unset MBEDTLS_HKDF_C # has independent PSA implementation
     scripts/config.py unset MBEDTLS_HMAC_DRBG_C