Remove authcrypt definition of TEST_NULL_ENTROPY

Remove the definition of the macros MBEDTLS_TEST_NULL_ENTROPY and
MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES if no entropy source is found while
compiling the authcrypt example.

Author: Andres AG

authcrypt/mbedtls_entropy_config.h

@@ -1,14 +1,24 @@
-#if !defined(MBEDTLS_ENTROPY_HARDWARE_ALT) && !defined(MBEDTLS_ENTROPY_NV_SEED)
-
-#ifdef MBEDTLS_TEST_NULL_ENTROPY
-#warning "MBED TLS SECURITY FEATURE IS DISABLED. THE TESTS WILL NOT BE SECURE! PLEASE IMPLEMENT HARDWARE ENTROPY FOR YOUR SELECTED HARDWARE."
-
-#else
-#warning "THIS HARDWARE DOES NOT HAVE ENTROPY. DISABLING MBED TLS SECURITY FEATURE."
-#define MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
-#define MBEDTLS_TEST_NULL_ENTROPY
-#warning "MBED TLS SECURITY FEATURE IS DISABLED. THE TESTS WILL NOT BE SECURE! PLEASE IMPLEMENT HARDWARE ENTROPY FOR YOUR SELECTED HARDWARE."
-#endif // defined(MBEDTLS_TEST_NULL_ENTROPY)
-
-#endif // !defined(MBEDTLS_ENTROPY_HARDWARE_ALT) && !defined(MBEDTLS_ENTROPY_NV_SEED)
+/*
+ *  Copyright (C) 2006-2016, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
 
+#if !defined(MBEDTLS_ENTROPY_HARDWARE_ALT) && \
+    !defined(MBEDTLS_ENTROPY_NV_SEED) && !defined(MBEDTLS_TEST_NULL_ENTROPY)
+#error "This hardware does not have an entropy source."
+#endif /* !MBEDTLS_ENTROPY_HARDWARE_ALT && !MBEDTLS_ENTROPY_NV_SEED &&
+        * !MBEDTLS_TEST_NULL_ENTROPY */