build: disable osxkeychain TPM backend by default

Change-Id: I3e121a7cee0451d20f83aa73742077bc621652be
diff --git a/tests/unit/security/tpm/back-end.t.cpp b/tests/unit/security/tpm/back-end.t.cpp
index cb0ec5d..0c4f87f 100644
--- a/tests/unit/security/tpm/back-end.t.cpp
+++ b/tests/unit/security/tpm/back-end.t.cpp
@@ -50,7 +50,7 @@
 BOOST_AUTO_TEST_SUITE(TestTpmBackEnd)
 
 using TestBackEnds = boost::mp11::mp_list<
-#if defined(NDN_CXX_HAVE_OSX_FRAMEWORKS) && defined(NDN_CXX_WITH_OSX_KEYCHAIN)
+#ifdef NDN_CXX_WITH_OSX_KEYCHAIN
   BackEndWrapperOsx,
 #endif
   BackEndWrapperMem,