[BOLT] Remove duplicate types (NFC)

This patch, a follow-up for 588628d,
removes duplicate types like T and PointerT in favor of reference and
pointer, respectively.

Author: kazutakahirata

bolt/include/bolt/Core/BinaryContext.h

@@ -107,8 +107,6 @@ template <typename ItrType,
 class FilterIterator {
   using inner_traits = std::iterator_traits<ItrType>;
   using Iterator = FilterIterator;
-  using T = typename std::iterator_traits<ItrType>::reference;
-  using PointerT = typename std::iterator_traits<ItrType>::pointer;
 
   PredType Pred;
   ItrType Itr, End;
@@ -139,8 +137,8 @@ class FilterIterator {
   Iterator operator--(int) { auto Tmp(Itr); prev(); return Tmp; }
   bool operator==(const Iterator &Other) const { return Itr == Other.Itr; }
   bool operator!=(const Iterator &Other) const { return !operator==(Other); }
-  T operator*() { return *Itr; }
-  PointerT operator->() { return &operator*(); }
+  reference operator*() { return *Itr; }
+  pointer operator->() { return &operator*(); }
   FilterIterator(PredType Pred, ItrType Itr, ItrType End)
       : Pred(Pred), Itr(Itr), End(End) {
     nextMatching();