Revert Decl's iterators back to pointer value_type rather than reference value_type

In addition, I've made the pointer and reference typedef 'void' rather than T*
just so they can't get misused. I would've omitted them entirely but
std::distance likes them to be there even if it doesn't use them.

This rolls back r155808 and r155869.

Review by Doug Gregor incorporating feedback from Chandler Carruth.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158104 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 2142102..a9092a4 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -5055,7 +5055,7 @@
 
   for (ObjCImplDecl::method_iterator
          I = ImplD->meth_begin(), E = ImplD->meth_end(); I != E; ++I)
-    Consumer->HandleInterestingDecl(DeclGroupRef(&*I));
+    Consumer->HandleInterestingDecl(DeclGroupRef(*I));
 
   Consumer->HandleInterestingDecl(DeclGroupRef(ImplD));
 }