Remove aom_simd.c and replace simd_check with macro

Change-Id: If2bb7ab2b16ba44e2d6e43eeb8713aa6c05d9d7c
diff --git a/aom_dsp/aom_simd.h b/aom_dsp/aom_simd.h
index ae4ff23..d830ce5 100644
--- a/aom_dsp/aom_simd.h
+++ b/aom_dsp/aom_simd.h
@@ -21,6 +21,8 @@
 #include "./aom_config.h"
 #include "./aom_simd_inline.h"
 
+#define SIMD_CHECK 1  // Sanity checks in C equivalents
+
 #if HAVE_NEON
 #include "simd/v256_intrinsics_arm.h"
 #elif HAVE_SSE2