vp9-rtc: Modify skip golden mode check for 1 layer
vp9-rtc: Modify skip golden mode check for 1 layer

For real-time CBR mode: golden reference mode testing is
skipped under certain conditons based on sse of zero-last mode.
This was done for svc mode. Here we add similar condition
for non-svc/1 layer encoding.

Reduces flashing block artifacts that can occur in background
areas with noise.

Change-Id: I93f71ea9507af8c9153fc6c0ba7dcc7a0fa8810d

webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx