Revert "Use a shared_ptr for our lock class"

This reverts commit cda7ff070863d72d4ad0b17737025d6f19a21c75.

Conflicts:
	task2/src/cuckooset.cpp
Don't delete old CuckooLock objects

On the one hand, we can't simply delete these since other threads might
still hold a reference and try to access these afterwards. On the other,
shared_ptr is not an option because it turns into the bottleneck.

As a first step, simply don't delete old locks and live with the memory
leak.
Delete old locks in ~CuckooLock()

Instead of simply leaking these, clean them up in our dtor. Also, first
usage of auto!
C++11 doesn't require a space between closing brackets
Further C++11 tweaks: ranged for loops