[MemorySSA] Don't sort IDF blocks.

Summary:
After r332167 we started to sort the IDF blocks inside IDF calculation, so
there is no need to re-sort them on the user site. The test changes are due to
a slightly different order we're using now (originally we used DFSInNumber and
now the blocks are sorted by a pair (LevelFromRoot, DFSInNumber)).

Reviewers: dberlin, mgrang

Subscribers: Prazek, hiraditya, george.burgess.iv, llvm-commits

Differential Revision: https://reviews.llvm.org/D46899

llvm-svn: 332385