[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

clang/lib/Serialization/Module.cpp

@@ -13,7 +13,6 @@
 //===----------------------------------------------------------------------===//
 #include "clang/Serialization/Module.h"
 #include "ASTReaderInternals.h"
-#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace clang;