Fix Make issues with Everest enabled

Apply Gilles suggestion to fix the problem with make on the CI when everest is enabled, i.e. use $(THIRDPARTY_DIR) instead of a fuzz specific hack involving $(THIRDPARTY_INCLUDES)

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/programs/Makefile b/programs/Makefile
index 82c8569..6baf465 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -114,7 +114,7 @@
 endif
 
 fuzz: ${MBEDTLS_TEST_OBJS}
-	$(MAKE) -C fuzz THIRDPARTY_INCLUDES=$(THIRDPARTY_INCLUDES)
+	$(MAKE) -C fuzz
 
 ${MBEDTLS_TEST_OBJS}:
 	$(MAKE) -C ../tests mbedtls_test