Could not find com.google.android.exoplayer:exoplayer:2.6.1.

Cannot build `Leanback` same - exoplayer seems to no longer be available.
Are there any plans to upgrade samples to exoplayer2?

```
Could not determine the dependencies of task ':app:preDebugBuild'.
> Could not resolve all task dependencies for configuration ':app:debugRuntimeClasspath'.
> Could not find com.google.android.exoplayer:exoplayer:2.6.1.
Searched in the following locations:
- file:/Users/gtalarico/Library/Android/sdk/extras/m2repository/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.pom
- file:/Users/gtalarico/Library/Android/sdk/extras/m2repository/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.jar
- file:/Users/gtalarico/Library/Android/sdk/extras/google/m2repository/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.pom
- file:/Users/gtalarico/Library/Android/sdk/extras/google/m2repository/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.jar
- file:/Users/gtalarico/Library/Android/sdk/extras/android/m2repository/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.pom
- file:/Users/gtalarico/Library/Android/sdk/extras/android/m2repository/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.jar
- https://dl.google.com/dl/android/maven2/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.pom
- https://dl.google.com/dl/android/maven2/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.jar
- https://repo.maven.apache.org/maven2/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.pom
- https://repo.maven.apache.org/maven2/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.jar
- https://jcenter.bintray.com/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.pom
- https://jcenter.bintray.com/com/google/android/exoplayer/exoplayer/2.6.1/exoplayer-2.6.1.jar
Required by:
project :app
> Could not find com.google.android.exoplayer:extension-leanback:2.6.1.
Searched in the following locations:
- file:/Users/gtalarico/Library/Android/sdk/extras/m2repository/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.pom
- file:/Users/gtalarico/Library/Android/sdk/extras/m2repository/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.jar
- file:/Users/gtalarico/Library/Android/sdk/extras/google/m2repository/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.pom
- file:/Users/gtalarico/Library/Android/sdk/extras/google/m2repository/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.jar
- file:/Users/gtalarico/Library/Android/sdk/extras/android/m2repository/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.pom
- file:/Users/gtalarico/Library/Android/sdk/extras/android/m2repository/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.jar
- https://dl.google.com/dl/android/maven2/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.pom
- https://dl.google.com/dl/android/maven2/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.jar
- https://repo.maven.apache.org/maven2/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.pom
- https://repo.maven.apache.org/maven2/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.jar
- https://jcenter.bintray.com/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.pom
- https://jcenter.bintray.com/com/google/android/exoplayer/extension-leanback/2.6.1/extension-leanback-2.6.1.jar
Required by:
project :app

Possible solution:
- Declare repository providing the artifact, see the documentation at https://docs.gradle.org/current/userguide/declaring_repositories.html
- ```

Start in the Leanback sample's app dependency configuration, where the build requests com.google.android.exoplayer:exoplayer and extension-leanback at 2.6.1; reproduce the :app:preDebugBuild failure first. Update the sample's ExoPlayer dependency usage as needed, and consider the work done when the Leanback sample resolves its dependencies and builds successfully.

Written by the indexing model from the issue text.