Use default temporal layers instead of the RealtimeTemporalLayers one.
When using low fps, having a single stream with much higher bitrate than
the lower simulcast stream causes poor rampup behavior.
Tested manually.
BUG=webrtc:4172
Review-Url: https://codereview.webrtc.org/2723983002
Cr-Commit-Position: refs/heads/master@{#16934}