[libFuzzer] replace std::random_shuffle with std::shuffle as std::random_shuffle is being deprecated in C++17. Also simplify fuzzer::Random. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294366 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed