ti: k3: common: Remove unused STUB macro

This macro was used when many of these functions were stubbed out,
the macro is not used anymore, remove it.
Signed-off-by: Andrew F. Davis <afd@ti.com>
Change-Id: Ida33f92fe3810a89e6e51faf6e93c1d2ada1a2ee

plat/ti/k3/common/k3_psci.c

@@ -20,8 +20,6 @@
 /* Need to flush psci internal locks before shutdown or their values are lost */
 #include "../../../../lib/psci/psci_private.h"
 
-#define STUB() ERROR("stub %s called\n", __func__)
-
 uintptr_t k3_sec_entrypoint;
 
 static void k3_cpu_standby(plat_local_state_t cpu_state)