Remove otPlat*Init() functions that are no longer used. (#142)

include/platform/alarm.h

@@ -52,11 +52,6 @@ extern "C" {
  *
  */
 
-/**
- * Initialize the Alarm.
- */
-void otPlatAlarmInit(void);
-
 /**
  * Set the alarm to fire at @p aDt milliseconds after @p aT0.
  *

include/platform/random.h

@@ -52,12 +52,6 @@ extern "C" {
  *
  */
 
-/**
- * Initialize the true random number generator.
- *
- */
-void otPlatRandomInit(void);
-
 /**
  * Get a 32-bit true random value.
  *