Fixes the MSVC build.

Commit r152704 exposed a latent MSVC limitation (aka bug). 
Both ilist and and iplist contains the same function:
  template<class InIt> void insert(iterator where, InIt first, InIt last) {
    for (; first != last; ++first) insert(where, *first);
  }

Also ilist inherits from iplist and ilist contains a "using iplist<NodeTy>::insert".
MSVC doesn't know which one to pick and complain with an error.

I think it is safe to delete ilist::insert since it is redundant anyway.

llvm-svn: 152746

llvm/include/llvm/ADT/ilist.h

@@ -652,10 +652,6 @@ struct ilist : public iplist<NodeTy> {
   void push_front(const NodeTy &val) { insert(this->begin(), val); }
   void push_back(const NodeTy &val) { insert(this->end(), val); }
 
-  // Special forms of insert...
-  template<class InIt> void insert(iterator where, InIt first, InIt last) {
-    for (; first != last; ++first) insert(where, *first);
-  }
   void insert(iterator where, size_type count, const NodeTy &val) {
     for (; count != 0; --count) insert(where, val);
   }