odintrin: drop duplicate define

Change-Id: I846cd0c4f5e3d60c76b969183d17ce11e6ba2999

av1/common/odintrin.h

@@ -250,9 +250,6 @@ typedef int32_t od_val32;
 # define OD_MULT16_16_Q15(a, b) \
   (((int16_t)(a)*((int32_t)(int16_t)(b))) >> 15)
 
-/* Multiplies 16-bit a by 32-bit b and keeps bits [16:47]. */
-# define OD_MULT16_32_Q16(a, b) ((int16_t)(a)*(int64_t)(int32_t)(b) >> 16)
-
 #ifdef __cplusplus
 }  // extern "C"
 #endif