Downgrade targetSdkVersion back to 28

- The upgrade to version 29 made Robolectric version 4.3 fail.
- Upgrading Robolectric to 4.3.1 requires Java 9, which requires manual
  configuration in Android Studio.

PiperOrigin-RevId: 281753915

constants.gradle

@@ -16,7 +16,7 @@ project.ext {
     releaseVersion = '2.11.0'
     releaseVersionCode = 2011000
     minSdkVersion = 16
-    targetSdkVersion = 29
+    targetSdkVersion = 28
     compileSdkVersion = 29
     dexmakerVersion = '2.21.0'
     mockitoVersion = '2.25.0'

demos/main/src/main/AndroidManifest.xml

@@ -34,7 +34,6 @@
       android:banner="@drawable/ic_banner"
       android:largeHeap="true"
       android:allowBackup="false"
-      android:requestLegacyExternalStorage="true"
       android:name="com.google.android.exoplayer2.demo.DemoApplication"
       tools:ignore="UnusedAttribute">
 

demos/surface/build.gradle

@@ -26,7 +26,7 @@ android {
         versionName project.ext.releaseVersion
         versionCode project.ext.releaseVersionCode
         minSdkVersion 29
-        targetSdkVersion project.ext.targetSdkVersion
+        targetSdkVersion 29
     }
 
     buildTypes {