function resetDecodingInfos(manifest) {
  if (!manifest) {
    return;
  }

  for (const variant of manifest.variants) {
    variant.decodingInfos = [];
  }
}
Because our MediaCapabilities integration adds decoding info to each variant,
we need to be careful to reset this info on variants that are cached and
persist between tests and between manifest parser instances.  This ensures
that these unusual test variants will not have persistent decoding infos from
MediaCapabilities.

For encrypted content, the decoding info contains negotiated EME information
which varies based on the chosen key system and whether the content will be
streamed or stored offline.  If one test loads the content for streaming,
then another test loads the same content for offline storage, the second test
would encounter the cached decoding info from the first test, and the
negotiated key system would not be set up for the correct session types.
This would lead to a test failure.  This sort of failure would not be seen in
real playback (since no supported manifest parser would ever cache variants).

By resetting variant.decodingInfos when the fake manifest parser is stopped,
we ensure that each test gets a clean slate (as would happen with a real
parser), and the correct decodingInfos show up for each part of each test
case.

@param {?shaka.extern.Manifest} manifest