Replace is_single_inter_mode with is_inter_singleref_mode
Replace is_single_inter_mode with is_inter_singleref_mode

BUG=aomedia:2044

Change-Id: I28adcc76c937ae760220779afa29c6cfaafce61a

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