[lld] Replace Symbolize.h with DIContext.h in lld's COFF lib

[noajshu]

Summary

lld only needs DIContext.h which it gets through Symbolize.h -> SymbolizableModule.h -> DIContext.h. This replaces it with a direct include of DIContext.h to avoid any confusion and pulling in unnecessary headers.

[phosek]

LGTM

lld/COFF/SymbolTable.cpp

 #include "Config.h"
 #include "Driver.h"
 #include "LTO.h"
 #include "PDB.h"
 #include "Symbols.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
 #include "lld/Common/Timer.h"
-#include "llvm/DebugInfo/Symbolize/Symbolize.h"
+#include "llvm/DebugInfo/DIContext.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/Object/WindowsMachineFlag.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include <utility>
 
 using namespace llvm;