h274: remove optimization pragma

This results in warnings on compilers which don't support it,
objections were raised during the review process about it but went unnoticed,
and the speed benefit is highly compiler and version specific, and
also not very critical.

We generally hand-write assembly to optimize loops like that, rather
than use compiler magic, and for 40% best case scenario, it's simply
not worth it.

Plus, tree vectorization is still problematic with GCC and disabled by default
for a good reason, so enabling it locally is sketchy.

libavcodec/h274.c

@@ -30,10 +30,6 @@
 
 #include "h274.h"
 
-// The code in this file has a lot of loops that vectorize very well, this is
-// about a 40% speedup for no obvious downside.
-#pragma GCC optimize("tree-vectorize")
-
 static const int8_t Gaussian_LUT[2048+256];
 static const uint32_t Seed_LUT[256];
 static const int8_t R64T[64][64];