Stop using VideoCodec.targetBitrate for vp8 screenshare config

This is a step toward simplifying the VideoCodec struct and removing the
targetBitrate. The hard-coded values now reside in
SimulcastRateAllocator.

A follow-up will do away with the field altogether.

Bug: webrtc:9504
Change-Id: I74d483682309d363048fbbbd31e0607d7242f504
Reviewed-on: https://webrtc-review.googlesource.com/87424
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23876}
diff --git a/modules/video_coding/video_codec_initializer_unittest.cc b/modules/video_coding/video_codec_initializer_unittest.cc
index 4edf31a..9b3cf3e 100644
--- a/modules/video_coding/video_codec_initializer_unittest.cc
+++ b/modules/video_coding/video_codec_initializer_unittest.cc
@@ -28,7 +28,7 @@
 static const uint32_t kDefaultMaxBitrateBps = 2000000;
 static const uint32_t kDefaultMinTransmitBitrateBps = 400000;
 static const int kDefaultMaxQp = 48;
-static const uint32_t kScreenshareTl0BitrateBps = 100000;
+static const uint32_t kScreenshareTl0BitrateBps = 200000;
 static const uint32_t kScreenshareCodecTargetBitrateBps = 200000;
 static const uint32_t kScreenshareDefaultFramerate = 5;
 // Bitrates for the temporal layers of the higher screenshare simulcast stream.