Don't clean test_keys.h and test_certs.h

This is in keeping with other generated files (such as generated .data
files) that are added to releases.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/Makefile b/tests/Makefile
index 8af23cf..14c6995 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -212,8 +212,7 @@
 clean:
 ifndef WINDOWS
 	rm -rf $(BINARIES) *.c *.datax
-	rm -f src/*.o src/drivers/*.o src/test_helpers/*.o src/libmbed* src/test_keys.h src/test_certs.h
-	rm -f src/test_keys.h src/test_certs.h
+	rm -f src/*.o src/drivers/*.o src/test_helpers/*.o src/libmbed*
 	rm -f include/test/instrument_record_status.h
 	rm -f include/alt-extra/*/*_alt.h
 	rm -rf libtestdriver1
@@ -224,8 +223,6 @@
 	if exist *.datax del /Q /F *.datax
 	if exist src/*.o del /Q /F src/*.o
 	if exist src/drivers/*.o del /Q /F src/drivers/*.o
-	if exist src/test_keys.h del /Q /F src/test_keys.h
-	if exist src/test_certs.h del /Q /F src/test_certs.h
 	if exist src/test_helpers/*.o del /Q /F src/test_helpers/*.o
 	if exist src/libmbed* del /Q /F src/libmbed*
 	if exist include/test/instrument_record_status.h del /Q /F include/test/instrument_record_status.h