Removing unneded extern declaration of a callback and including common.h where the cb is needed

Signed-off-by: TRodziewicz <tomasz.rodziewicz@mobica.com>
diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index 80c730b..6a87e80 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -24,6 +24,7 @@
 #endif
 
 #include "mbedtls/build_info.h"
+#include "common.h"
 
 /* Test code may use deprecated identifiers only if the preprocessor symbol
  * MBEDTLS_TEST_DEPRECATED is defined. When building tests, set