DebugSubsectionVisitor.h - remove unnecessary includes/forward declarations. NFC.

We don't need the StringsAndChecksumsRef forward declaration as we have to include StringsAndChecksums.h.
We don't need DebugSubsectionRecord.h and we forward declare all referenced classes.
We don't need to include cstdint as we don't use any stdint types.

Author: RKSimon

llvm/include/llvm/DebugInfo/CodeView/DebugSubsectionVisitor.h

@@ -10,10 +10,8 @@
 #define LLVM_DEBUGINFO_CODEVIEW_MODULEDEBUGFRAGMENTVISITOR_H
 
 #include "llvm/DebugInfo/CodeView/CodeView.h"
-#include "llvm/DebugInfo/CodeView/DebugSubsectionRecord.h"
 #include "llvm/DebugInfo/CodeView/StringsAndChecksums.h"
 #include "llvm/Support/Error.h"
-#include <cstdint>
 
 namespace llvm {
 
@@ -30,7 +28,6 @@ class DebugStringTableSubsectionRef;
 class DebugSymbolRVASubsectionRef;
 class DebugSymbolsSubsectionRef;
 class DebugUnknownSubsectionRef;
-class StringsAndChecksumsRef;
 
 class DebugSubsectionVisitor {
 public: