Rename the 'no entropy' feature to MBEDTLS_TEST_NULL_ENTROPY

Following review and for clarity, changed the name of the feature to 'null
entropy'.
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index b9ba6c5..209c106 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -265,10 +265,10 @@
 scripts/config.pl set MBEDTLS_NO_PLATFORM_ENTROPY # uses syscall() on GNU/Linux
 CC=gcc CFLAGS='-Werror -O0 -std=c99 -pedantic' make lib
 
-msg "build: default config with  MBEDTLS_TEST_WO_ENTROPY (ASan build)"
+msg "build: default config with  MBEDTLS_TEST_NULL_ENTROPY (ASan build)"
 cleanup
 cp "$CONFIG_H" "$CONFIG_BAK"
-scripts/config.pl set MBEDTLS_TEST_WO_ENTROPY
+scripts/config.pl set MBEDTLS_TEST_NULL_ENTROPY
 scripts/config.pl set MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
 scripts/config.pl set MBEDTLS_ENTROPY_C
 scripts/config.pl unset MBEDTLS_ENTROPY_NV_SEED
@@ -277,7 +277,7 @@
 CC=gcc cmake -D CMAKE_C_FLAGS:String="-fsanitize=address -fno-common -O3" .
 make
 
-msg "test: MBEDTLS_TEST_WO_ENTROPY - main suites and selftest (ASan build)"
+msg "test: MBEDTLS_TEST_NULL_ENTROPY - main suites and selftest (ASan build)"
 make test
 programs/test/selftest