Revert "add #respond_to? support to the delegator"

This realisation causes a deadlock when Rails try to run finder callbacks.
Also there's no need to redefine ```#respond_to?``` method at all. We should use explicit delegation with standard ```.delegate``` method if we need an object both to delegate & respond to the call.
So, it was a mistake to redefine ```#respond_to?``` and the fix is just this revert.