DI: Use new 'self initialized' analysis in conditional destroy lowering

This changes code generation a bit, because now the conditional
state bitmap uses a bit to track if the 'self' box was stored,
not if the 'self' value was consumed. In some cases, this
eliminates an extra bit, in other places it introduces an
extra bit, but it really doesn't matter because LLVM will
optimize this bit manipulation easily.

Author: slavapestov