Disable THREADING on embedded aarch64

With THREADING enabled, you get a NoThreadError at startup
when using the classes unit.

rtl/embedded/system.cfg

@@ -102,7 +102,7 @@
 -SfRTTI
 -SfWIDESTRINGS
 -SfDYNARRAYS
--SfTHREADING
+#-SfTHREADING
 -SfVARIANTS
 -SfOBJECTS
 -SfCOMMANDARGS