fix scopes loading when serializing

rails 2 doesn't know about respond_to_missing? in ruby 1.9, so
Marshal.dump(User.where("syntax error")) calls respond_to?, which
chains to respond_to_missing?, which Rails 2 delegated to proxy_found,
thinking it was a useful instance method from Array

simply removing the delegated method and letting the default
implementation return false is sufficient

Change-Id: I6fe4b4daf5fa5b4a4489c8aedaa711945bb764ed
Reviewed-on: https://gerrit.instructure.com/28906
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>