Hide ExoCastPlayer components again

This CL is effectively a rollback of cr/233072247.

PiperOrigin-RevId: 233793032

RELEASENOTES.md

@@ -2,10 +2,6 @@
 
 ### dev-v2 (not yet released) ###
 
-* Add `ExoCastPlayer` to cast to custom receiver apps using ExoPlayer's custom
-  communication protocol
-  ([#5486](https://github.com/google/ExoPlayer/issues/5486)). Also update the
-  Cast demo app to work with `ExoCastPlayer`.
 * HLS:
   * Form an adaptive track group out of audio renditions with matching name.
 * DASH:

demos/cast/build.gradle

@@ -51,11 +51,6 @@ android {
     flavorDimensions "receiver"
 
     productFlavors {
-        exoCast {
-            dimension "receiver"
-            manifestPlaceholders =
-                    [castOptionsProvider: "com.google.android.exoplayer2.ext.cast.ExoCastOptionsProvider"]
-        }
         defaultCast {
             dimension "receiver"
             manifestPlaceholders =