Revert "[BPI] Use a safer constructor to calculate branch probabilities"

This reverts commit r290016. It breaks this bot, even though the test
passes locally:

  http://bb.pgr.jp/builders/ninja-x64-msvc-RA-centos6/builds/32956/

AnalysisTests: /home/bb/ninja-x64-msvc-RA-centos6/llvm-project/llvm/lib/Support/BranchProbability.cpp:52: static llvm::BranchProbability llvm::BranchProbability::getBranchProbability(uint64_t, uint64_t): Assertion `Numerator <= Denominator && "Probability cannot be bigger than 1!"' failed.
llvm-svn: 290019