Remove MBEDTLS_TEST_NULL_ENTROPY config option.

Building the library without entropy sources negates any and all security
provided by the library.
This option was originally requested a relatively long time ago and it
does not provide any tangible benefit for users any more.

Signed-off-by: Mateusz Starzyk <mateusz.starzyk@mobica.com>
diff --git a/tests/suites/test_suite_random.function b/tests/suites/test_suite_random.function
index 37fa36e..c532c8a 100644
--- a/tests/suites/test_suite_random.function
+++ b/tests/suites/test_suite_random.function
@@ -18,7 +18,7 @@
 
 /* END_HEADER */
 
-/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:!MBEDTLS_TEST_NULL_ENTROPY:MBEDTLS_CTR_DRBG_C */
+/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:MBEDTLS_CTR_DRBG_C */
 void random_twice_with_ctr_drbg( )
 {
     mbedtls_entropy_context entropy;
@@ -57,7 +57,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:!MBEDTLS_TEST_NULL_ENTROPY:MBEDTLS_HMAC_DRBG_C */
+/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:MBEDTLS_HMAC_DRBG_C */
 void random_twice_with_hmac_drbg( int md_type )
 {
     mbedtls_entropy_context entropy;
@@ -97,7 +97,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_TEST_NULL_ENTROPY:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
+/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 void random_twice_with_psa_from_classic( )
 {
     unsigned char output1[OUTPUT_SIZE];
@@ -123,7 +123,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_TEST_NULL_ENTROPY:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
+/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 void random_twice_with_psa_from_psa( )
 {
     unsigned char output1[OUTPUT_SIZE];