Rename aom_lpf_horizontal_edge_8() to aom_lpf_horizontal_16().
Rename aom_lpf_horizontal_edge_16() to aom_lpf_horizontal_16_dual().

based on the same change from libvpx:
7f1f35183 Unify loopfilter function names

Change-Id: I4fda7a2e3a893fc3dee0779975e2d4145c32f5d2