dlmalloc: remove unit test support in SPL

We cannot run unit tests in SPL. So remove the unit test support.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/common/dlmalloc.c b/common/dlmalloc.c
index dade68f..db5ab55 100644
--- a/common/dlmalloc.c
+++ b/common/dlmalloc.c
@@ -1,6 +1,6 @@
 #include <common.h>
 
-#if defined(CONFIG_UNIT_TEST)
+#if CONFIG_IS_ENABLED(UNIT_TEST)
 #define DEBUG
 #endif