AccountManager: Fix comment that talks about account_external_ids table

This table doesn't exist anymore. External IDs are now stored in NoteDb.

Change-Id: I482fd197da82ca510b65ae55f901315f670ea696
Signed-off-by: Edwin Kempin <ekempin@google.com>

gerrit-server/src/main/java/com/google/gerrit/server/account/AccountManager.java

@@ -329,8 +329,7 @@ public class AccountManager {
       // setting the given user name has failed, but the realm does not
       // allow the user to manually set a user name,
       // this means we would end with an account without user name
-      // (without 'username:<USERNAME>' entry in
-      // account_external_ids table),
+      // (without 'username:<USERNAME>' external ID),
       // such an account cannot be used for uploading changes,
       // this is why the best we can do here is to fail early and cleanup
       // the database