[clang-tidy] Use unresolvedLookupExpr node matcher from ASTMatcher.

[aaron.ballman]

LGTM!

clang-tidy/misc/UnusedUsingDeclsCheck.cpp

 //===--- UnusedUsingDeclsCheck.cpp - clang-tidy----------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "UnusedUsingDeclsCheck.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
-#include "clang/ASTMatchers/ASTMatchersInternal.h"
 #include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
 
 namespace clang {
 namespace tidy {
 namespace misc {
 
-namespace {
-// FIXME: Move this node matcher to ASTMatcher.
-const internal::VariadicDynCastAllOfMatcher<Stmt, UnresolvedLookupExpr>
-    unresolvedLookupExpr;
-}
-
 void UnusedUsingDeclsCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(usingDecl(isExpansionInMainFile()).bind("using"), this);
   auto DeclMatcher = hasDeclaration(namedDecl().bind("used"));
   Finder->addMatcher(loc(recordType(DeclMatcher)), this);
   Finder->addMatcher(loc(templateSpecializationType(DeclMatcher)), this);
   Finder->addMatcher(declRefExpr().bind("used"), this);
   Finder->addMatcher(callExpr(callee(unresolvedLookupExpr().bind("used"))),
                      this);