mpegvideo: drop support for real (non-emulated) edges

Several decoders disable those anyway and they are not measurably faster
on x86. They might be somewhat faster on other platforms due to missing
emu edge SIMD, but the gain is not large enough (and those decoders
relevant enough) to justify the added complexity.
vp8: drop support for real (non-emulated) edges

They are not measurably faster on x86, they might be somewhat faster on
other platforms due to missing emu edge SIMD, but the gain is not large
enough to justify the added complexity.
vp9: drop support for real (non-emulated) edges

They are not measurably faster on x86, they might be somewhat faster on
other platforms due to missing emu edge SIMD, but the gain is not large
enough to justify the added complexity.
FATE: add MSS2 tests
hevc: fix decoding of one PU wide files

For those the block size may be larger than the source linesize (if the
edges are not allocated).

Signed-off-by: Anton Khirnov <anton@khirnov.net>