Revert r330403 and r330413.

Revert r330413: "[SSAUpdaterBulk] Use SmallVector instead of DenseMap for storing rewrites."
Revert r330403 "Reapply "[PR16756] Use SSAUpdaterBulk in JumpThreading." one more time."

r330403 commit seems to crash clang during our integrate while doing PGO build with the following stacktrace:
      #2 llvm::SSAUpdaterBulk::RewriteAllUses(llvm::DominatorTree*, llvm::SmallVectorImpl<llvm::PHINode*>*)
      #3 llvm::JumpThreadingPass::ThreadEdge(llvm::BasicBlock*, llvm::SmallVectorImpl<llvm::BasicBlock*> const&, llvm::BasicBlock*)
      #4 llvm::JumpThreadingPass::ProcessThreadableEdges(llvm::Value*, llvm::BasicBlock*, llvm::jumpthreading::ConstantPreference, llvm::Instruction*)
      #5 llvm::JumpThreadingPass::ProcessBlock(llvm::BasicBlock*)
The crash happens while compiling 'lib/Analysis/CallGraph.cpp'.

r3340413 is reverted due to conflicting changes.

llvm-svn: 330416