swresample/x86/rematrix: Remove obsolete MMX functions

x64 always has MMX, MMXEXT, SSE and SSE2 and this means
that some functions for MMX, MMXEXT and 3dnow are always
overridden by other functions (unless one e.g. explicitly
disables SSE2) for x64. So given that the only systems that
benefit from these functions are truely ancient 32bit x86s
they are removed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libswresample/x86/rematrix.asm

@@ -223,12 +223,6 @@ mix_2_1_int16_u_int %+ SUFFIX:
 %endmacro
 
 
-INIT_MMX mmx
-MIX1_INT16 u
-MIX1_INT16 a
-MIX2_INT16 u
-MIX2_INT16 a
-
 INIT_XMM sse
 MIX2_FLT u
 MIX2_FLT a

libswresample/x86/rematrix_init.c

@@ -28,7 +28,6 @@ mix_2_1_func_type ff_mix_2_1_a_## type ## _ ## simd;
 
 D(float, sse)
 D(float, avx)
-D(int16, mmx)
 D(int16, sse2)
 
 av_cold int swri_rematrix_init_x86(struct SwrContext *s){
@@ -43,10 +42,6 @@ av_cold int swri_rematrix_init_x86(struct SwrContext *s){
     s->mix_2_1_simd = NULL;
 
     if (s->midbuf.fmt == AV_SAMPLE_FMT_S16P){
-        if(EXTERNAL_MMX(mm_flags)) {
-            s->mix_1_1_simd = ff_mix_1_1_a_int16_mmx;
-            s->mix_2_1_simd = ff_mix_2_1_a_int16_mmx;
-        }
         if(EXTERNAL_SSE2(mm_flags)) {
             s->mix_1_1_simd = ff_mix_1_1_a_int16_sse2;
             s->mix_2_1_simd = ff_mix_2_1_a_int16_sse2;