[Index] Remove unused includes (NFC) (#142525)

These are identified by misc-include-cleaner.  I've filtered out those
that break builds.  Also, I'm staying away from llvm-config.h,
config.h, and Compiler.h, which likely cause platform- or
compiler-specific build failures.

Author: kazutakahirata

clang/lib/Index/CommentToXML.cpp

@@ -11,7 +11,6 @@
 #include "clang/AST/Attr.h"
 #include "clang/AST/Comment.h"
 #include "clang/AST/CommentVisitor.h"
-#include "clang/Basic/FileManager.h"
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Format/Format.h"

clang/lib/Index/FileIndexRecord.cpp

@@ -7,10 +7,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "FileIndexRecord.h"
-#include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/Basic/SourceManager.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/Support/Path.h"
 
 using namespace clang;

clang/lib/Index/IndexingAction.cpp

@@ -10,12 +10,10 @@
 #include "IndexingContext.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendAction.h"
-#include "clang/Frontend/MultiplexConsumer.h"
 #include "clang/Index/IndexDataConsumer.h"
 #include "clang/Lex/PPCallbacks.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Serialization/ASTReader.h"
-#include "llvm/ADT/STLExtras.h"
 #include <memory>
 
 using namespace clang;

clang/lib/Index/USRGeneration.cpp

@@ -13,7 +13,6 @@
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/DeclVisitor.h"
 #include "clang/AST/ODRHash.h"
-#include "clang/Basic/FileManager.h"
 #include "clang/Lex/PreprocessingRecord.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"