Revert r316582 [Local] Fix a bug in the domtree update logic for MergeBasicBlockIntoOnlyPred.

Summary: This reverts commit r316582. It looks like this commit broke tests on one buildbot:
http://lab.llvm.org:8011/builders/llvm-clang-x86_64-expensive-checks-win/builds/5719

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Failing Tests (1):
    LLVM :: Transforms/CalledValuePropagation/simple-arguments.ll

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316612 91177308-0d34-0410-b5e6-96231b3b80d8