Remove media3-only line from exoplayer2 `build.gradle` file

#minor-release

PiperOrigin-RevId: 470999044
(cherry picked from commit 932f0d22)

libraries/transformer/build.gradle

@@ -30,7 +30,7 @@ android {
     }
 
     sourceSets {
-        androidTest.assets.srcDir '../test_data/src/test/assets/' //copybara:media3-only
+        androidTest.assets.srcDir '../test_data/src/test/assets/'
         test.assets.srcDir '../test_data/src/test/assets/'
     }
 }