Remove seemingly unused dependency

PiperOrigin-RevId: 266802447

demos/cast/build.gradle

@@ -57,7 +57,6 @@ dependencies {
     implementation project(modulePrefix + 'library-ui')
     implementation project(modulePrefix + 'extension-cast')
     implementation 'androidx.appcompat:appcompat:1.0.2'
-    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
     implementation 'androidx.recyclerview:recyclerview:1.0.0'
     implementation 'com.google.android.material:material:1.0.0'
 }