[clang] Remove unused SourceManager.cpp includes, NFC (trying out clangd)

Author: rnk

clang/lib/Basic/SourceManager.cpp

@@ -24,15 +24,11 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Allocator.h"
-#include "llvm/Support/AutoConvert.h"
 #include "llvm/Support/Capacity.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/FileSystem.h"
-#include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>