Does Steel Hellkite destroy cards in my opponent's library and hand?
The key word here is "permanent", which in the game of Magic essentially means "a card or token that's on the battlefield".  Cards in someone's library are never counted as being "permanents".

MTG Comprehensive Rules, 110.1:


  A permanent is a card or token on the battlefield. A permanent remains
  on the battlefield indefinitely. A card or token becomes a permanent
  as it enters the battlefield and it stops being a permanent as it's
  moved to another zone by an effect or rule.


Also note that "converted mana cost" has nothing to do with being a 2/2 creature.  There are quite a number of things that cost 2 mana that are also 2/2 creatures, but not all 2/2 creatures "have a converted mana cost of 2", by any means!