ARM: bswap: drop armcc version of av_bswap16()

This function causes several versions of armcc to miscompile code,
and the performance impact is small.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavutil/arm/bswap.h

@@ -26,13 +26,6 @@
 #ifdef __ARMCC_VERSION
 
 #if HAVE_ARMV6
-#define av_bswap16 av_bswap16
-static av_always_inline av_const unsigned av_bswap16(unsigned x)
-{
-    __asm { rev16 x, x }
-    return x;
-}
-
 #define av_bswap32 av_bswap32
 static av_always_inline av_const uint32_t av_bswap32(uint32_t x)
 {