dsputil_init() is deprecated and not meant to be exported.
ff_dsputil_init() is internal to libavcodec and thus can not be used.
avpriv_dsputil_init() is the version shared between libraries.
This commit fixes 3 unjustified libavfilter deprecated warnings.
The next commit will introduce a proper decimation filter to be used
along with the field matching filter. To avoid confusion with this
filter which has currently a very limited usage (and will not work
properly with the fieldmatching filter), the new decimation filter will
take the decimate name, and this filter is renamed to mpdecimate.