Deprecation warning for `manifest.dash.manifestPreprocessor` is always logged

[absidue]

Have you read the FAQ and checked for duplicate open issues?
Yes

If the problem is related to FairPlay, have you read the tutorial?

Not applicable

What version of Shaka Player are you using?

4.8.0

Can you reproduce the issue with our latest release version?
Yes

Can you reproduce the issue with the latest code from main?
Not tested

Are you using the demo app or your own custom app?
Custom, demo app is still using 4.7.11

If custom app, can you reproduce the issue using our demo app?
No, demo app hasn't been upgraded to 4.8.0 yet.

What browser and OS are you using?
Firefox, Windows 10

For embedded devices (smart TVs, etc.), what model and firmware version are you using?
Not applicable

What are the manifest and license server URIs?

Happens with all DASH manifests

What configuration are you using? What is the output of player.getConfiguration()?

Default

What did you do?

Load a DASH manifest with shaka-player 4.8.0

What did you expect to happen?
No deprecation messages to be logged for configuration options, as I'm using the default ones.

What actually happened?

A deprecation message for manifest.dash.manifestPreprocessor gets logged every time a DASH manifest is loaded.

Taking a quick look at the source code, shaka-player sets manifest.dash.manifestPreprocessor to a function here: https://github.com/shaka-project/shaka-player/blob/v4.8.0/lib/util/player_configuration.js#L144, so even if the user hasn't set the option themselves, it will always have a value when it gets to here: https://github.com/avelad/shaka-player/blob/v4.8.0/lib/dash/dash_parser.js#L341 which results in the backwards compatibility code running and logging the depreciation notice.