cpu/lpc1768: remove useless timer periph file guard

cpu/lpc1768/periph/timer.c

@@ -24,9 +24,6 @@
 #include "periph_conf.h"
 #include "periph/timer.h"
 
-/* guard file in case no timers are defined */
-#if TIMER_0_EN
-
 /**
  * @name Timer channel interrupt flags
  * @{
@@ -148,5 +145,3 @@ void TIMER_0_ISR(void)
     cortexm_isr_end();
 }
 #endif
-
-#endif /* TIMER_0_EN */