AP_Common: simplify ARRAY_SIZE

This rolls back to the simpler version of ARRAY_SIZE. The more complex
one helps catching bugs when we use pointers when we are expecting an
array, but can't stand arrays with 0 elements.  I'm not aware of bugs it
actually caught on ArduPilot, although it did for me in other projects.

I think this is better than having a separate "_SIMPLE" version of the
macro and spread its usage... the trend is just to use the simpler
version anyway.

libraries/AP_Common/AP_Common.h

@@ -71,13 +71,7 @@
 #define LOWBYTE(i) ((uint8_t)(i))
 #define HIGHBYTE(i) ((uint8_t)(((uint16_t)(i))>>8))
 
-template <typename T, size_t N>
-char (&_ARRAY_SIZE_HELPER(T (&_arr)[N]))[N];
-
-template <typename T>
-char (&_ARRAY_SIZE_HELPER(T (&_arr)[0]))[0];
-
-#define ARRAY_SIZE(_arr) sizeof(_ARRAY_SIZE_HELPER(_arr))
+#define ARRAY_SIZE(_arr) (sizeof(_arr) / sizeof(_arr[0]))
 
 // simpler ARRAY_SIZE which can handle zero elements
 #define ARRAY_SIZE_SIMPLE(_arr) (sizeof(_arr)/sizeof(_arr[0]))