EME: Address TODOs related to the removal of prefixed EME

media/base/android/java/src/org/chromium/media/MediaDrmBridge.java

Index: media/base/android/java/src/org/chromium/media/MediaDrmBridge.java
diff --git a/media/base/android/java/src/org/chromium/media/MediaDrmBridge.java b/media/base/android/java/src/org/chromium/media/MediaDrmBridge.java
index add05056accd59fbb60462ee059763266c32c228..25ffb1959d52985456972ff9fa1131370cac9bb5 100644
--- a/media/base/android/java/src/org/chromium/media/MediaDrmBridge.java
+++ b/media/base/android/java/src/org/chromium/media/MediaDrmBridge.java
@@ -752,9 +752,8 @@ public class MediaDrmBridge {
             return;
         }
 
-        // TODO(xhwang): DCHECK this now that prefixed EME is deprecated.
-        // https://crbug.com/249976
         if (!sessionExists(sessionId)) {
+            assert false; // Should never happen.
             onPromiseRejected(
                     promiseId, "Invalid session in updateSession: " + bytesToHexString(sessionId));
             return;