Rename aom_highbd_lpf_horizontal_edge_8() to aom_highbd_lpf_horizontal_16().
Rename aom_highbd_lpf_horizontal_edge_16() to aom_highbd_lpf_horizontal_16_dual().

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

Change-Id: I40cd587e74e0fe02bae23e6c10280c8e269df1d6