SSSE3 is already quite old (introduced 2006 for Intel, 2011 for AMD),
so that the overwhelming majority of our users (particularly those
that actually update their FFmpeg) will be using the SSSE3 version
of filter_line.
This commit therefore removes the overridden MMXEXT version
(which didn't abide by the ABI) which allows us to remove
an emms_c() from vf_gradfun.c, so that users with SSSE3 no longer
pay a price for the mere existence of an MMXEXT version.
Reviewed-by: Lynne <dev@lynne.ee>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
