Revert "Add the NullCheckElimination pass to the default pass list"

This reverts commit e1af108 as the pass
causes misoptimizations in certain situations.

lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -234,8 +234,6 @@ void PassManagerBuilder::populateModulePassManager(
  MPM.add(createEarlyCSEPass());              // Catch trivial redundancies
  MPM.add(createJumpThreadingPass());         // Thread jumps.
  MPM.add(createCorrelatedValuePropagationPass()); // Propagate conditionals
  // Specific to the rust-lang llvm branch:
  MPM.add(createNullCheckEliminationPass());  // Eliminate null checks
  MPM.add(createCFGSimplificationPass());     // Merge & remove BBs
  MPM.add(createInstructionCombiningPass());  // Combine silly seq's
  addExtensionsToPM(EP_Peephole, MPM);
@@ -278,8 +276,6 @@ void PassManagerBuilder::populateModulePassManager(
  addExtensionsToPM(EP_Peephole, MPM);
  MPM.add(createJumpThreadingPass());         // Thread jumps
  MPM.add(createCorrelatedValuePropagationPass());
  // Specific to the rust-lang llvm branch:
  MPM.add(createNullCheckEliminationPass());  // Eliminate null checks
  MPM.add(createDeadStoreEliminationPass());  // Delete dead stores
  MPM.add(createLICMPass());