test: remove leftover from past PR development

ECP_LIGHT was never set as public symbol so it should not be
enabled/disabled using the config.py script.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index a28cd28..9e2aa95 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2432,7 +2432,6 @@
         scripts/config.py unset MBEDTLS_ECJPAKE_C
         # Disable ECP module (entirely)
         scripts/config.py unset MBEDTLS_ECP_C
-        scripts/config.py unset MBEDTLS_ECP_LIGHT
     fi
 
     # Disable PK module since it depends on ECP