Revert "Diagnose UnresolvedLookupExprs that resolve to instance members in static methods"

This reverts commit r250592.

It has issues around unevaluated contexts, like this:
  template <class T> struct A { T i; };
  template <class T>
  struct B : A<T> {
    using A<T>::i;
    typedef decltype(i) U;
  };
  template struct B<int>;

llvm-svn: 250774