Include TICKLESS stack size increase even without LPTICKER_DELAY_TICKS

LPTICKER_DELAY_TICKS extra stack size has been introduced with the LP
ticker C++ wrapper. now we've removed the wrapper and LPTICKER_DELAY_TICKS
definition, but we still need extra stack size for the low level wrapper.

rtos/TARGET_CORTEX/mbed_rtx_conf.h

@@ -40,7 +40,7 @@
 #endif
 
 // Increase the idle thread stack size when tickless is enabled
-#if defined(MBED_TICKLESS) && defined(LPTICKER_DELAY_TICKS) && (LPTICKER_DELAY_TICKS > 0)
+#if defined(MBED_TICKLESS)
 #define EXTRA_IDLE_STACK MBED_CONF_RTOS_IDLE_THREAD_STACK_SIZE_TICKLESS_EXTRA
 #else
 #define EXTRA_IDLE_STACK 0