[NFC] Header cleanup

Summary: Removed unused headers, replaced some headers with forward class declarations

Patch by: Eugene <claprix@yandex.ru>

Differential Revision: https://reviews.llvm.org/D20100

llvm-svn: 275882
diff --git a/clang/lib/AST/AttrImpl.cpp b/clang/lib/AST/AttrImpl.cpp
index cb60870..b06b50c 100644
--- a/clang/lib/AST/AttrImpl.cpp
+++ b/clang/lib/AST/AttrImpl.cpp
@@ -11,11 +11,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/AST/Attr.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/Attr.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/Type.h"
-#include "llvm/ADT/StringSwitch.h"
 using namespace clang;
 
 #include "clang/AST/AttrImpl.inc"