[IR] Remove line causing build issues for VS2015

[dstuttard]

Summary

Change to add iterator and range accesor for the PHI nodes of basic block causes a build failure for
me on VS2015 (https://reviews.llvm.org/D33533)

It works on VS2017 so presumably this is a VS2015 limitation.

Removed the line to enable build. Is this required or is there an alternative way to implement it?

include/llvm/IR/BasicBlock.h

public:
     template <typename PHINodeU, typename BBIteratorU>
     phi_iterator_impl(const phi_iterator_impl<PHINodeU, BBIteratorU> &Arg)
         : PN(Arg.PN) {}
 
     bool operator==(const phi_iterator_impl &Arg) const { return PN == Arg.PN; }
 
     PHINodeT &operator*() const { return *PN; }
 
-    using phi_iterator_impl::iterator_facade_base::operator++;
     phi_iterator_impl &operator++() {
       assert(PN && "Cannot increment the end iterator!");
       PN = dyn_cast<PHINodeT>(std::next(BBIteratorT(PN)));
       return *this;
     }
   };
   typedef phi_iterator_impl<> phi_iterator;
   typedef phi_iterator_impl<const PHINode, BasicBlock::const_iterator>