Removed delete from CC_SAFE_DELETE and changed 0 to nullptr on all CC_SAFE macros

This implements this issue: https://github.com/cocos2d/cocos2d-x/issues/3099

I've also change all pointer assignments to 0 to assignments to nullptr on the CC_SAFE macros.
Also aligned them for better readability :)
Merge pull request #3269 from metalbass/patch-4

Removed if from CC_SAFE_DELETE and changed 0 to nullptr on all CC_SA...