Don't reset encoder on max/min bitrate change.

- Don't reset encoder if max/min bitrate changed.
- Removed min/max bitrate DCHECKs from encoder wrappers.
- Reset encoder if start_bitrate changed. Only do this if encoding
  has not yet started.
- Updated ReconfigureBitratesSetsEncoderBitratesCorrectly test.
- Removed EncoderSetupPropagatesCommonEncoderConfigValues test since it
was a subset of ReconfigureBitratesSetsEncoderBitratesCorrectly.

Bug: webrtc:10773
Change-Id: Id9cbb2ea229232fd95967819e2a937b26948de9f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/144028
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28446}

modules/video_coding/codecs/vp9/vp9_impl.cc

@@ -391,19 +391,9 @@ void VP9EncoderImpl::SetRates(const RateControlParameters& parameters) {
                         << parameters.framerate_fps;
     return;
   }
-  // Update bit rate
-  if (codec_.maxBitrate > 0 &&
-      parameters.bitrate.get_sum_kbps() > codec_.maxBitrate) {
-    RTC_LOG(LS_WARNING) << "Target bitrate exceeds maximum: "
-                        << parameters.bitrate.get_sum_kbps() << " vs "
-                        << codec_.maxBitrate;
-    return;
-  }
 
   codec_.maxFramerate = static_cast<uint32_t>(parameters.framerate_fps + 0.5);
   requested_rate_settings_ = parameters;
-
-  return;
 }
 
 // TODO(eladalon): s/inst/codec_settings/g.