Remove config include from header

core_mqtt_serializer.h included the user coreMQTT config, which spills
the config header's contents into all consumers of coreMQTT's headers.
Macros from the config are no longer used in the the API, so this is
also no longer used for anything, so can be removed.

source/include/core_mqtt_serializer.h

@@ -42,18 +42,6 @@
 #endif
 /* *INDENT-ON */
 
-/* MQTT_DO_NOT_USE_CUSTOM_CONFIG allows building the MQTT library
- * without a custom config. If a custom config is provided, the
- * MQTT_DO_NOT_USE_CUSTOM_CONFIG macro should not be defined. */
-#ifndef MQTT_DO_NOT_USE_CUSTOM_CONFIG
-    /* Include custom config file before other headers. */
-    #include "core_mqtt_config.h"
-#endif
-
-/* Include config defaults header to get default values of configs not
- * defined in core_mqtt_config.h file. */
-#include "core_mqtt_config_defaults.h"
-
 #include "transport_interface.h"
 
 /* MQTT packet types. */

test/unit-test/core_mqtt_utest.c

@@ -38,6 +38,8 @@
 #include "mock_core_mqtt_serializer.h"
 #include "mock_core_mqtt_state.h"
 
+#include "core_mqtt_config_defaults.h"
+
 /* Set network context to double pointer to buffer (uint8_t**). */
 struct NetworkContext
 {