Database: Fix misleading documentation in childByAutoId (#10217)

FirebaseDatabase/Sources/Public/FirebaseDatabase/FIRDatabaseReference.h

@@ -57,9 +57,8 @@ NS_SWIFT_NAME(DatabaseReference)
  * FIRDatabaseReference to it. This is useful when the children of a Firebase
  * Database location represent a list of items.
  *
- * The unique key generated by childByAutoId: is prefixed with a
- * client-generated timestamp so that the resulting list will be
- * chronologically-sorted.
+ * The unique key generated by childByAutoId: is based on a client-generated
+ * timestamp so that the resulting list will be chronologically-sorted.
  *
  * @return A FIRDatabaseReference for the generated location.
  */