[NORMATIVE, segment-pred-last] Fix segfeatures_copy
[NORMATIVE, segment-pred-last] Fix segfeatures_copy

Previously, segfeatures_copy was calling
segfeature_active(src, <segment id>, <feature>)
to determine if a particular feature was active in the source
features.

The issue with this is that, when we copy segment features, we
don't copy seg->enabled, as it shouldn't be needed anywhere.
This means that src->enabled might be 0 even if the frame it
came from used segmentation!

The solution is to ignore src->enabled, and to directly check
that the feature of interest is enabled.

BUG=aomedia:1621

Change-Id: Ic34c52594a3d31ef65146a6ba55ec6d7ab9fb8fc

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom