[clang][lex] NFC: Remove unused HeaderFileInfo member

[jansvoboda11]

Summary

This patch removes HeaderFileInfo::isNonDefault, which is not being used anywhere.

[dexonsmith]

LGTM.

clang/include/clang/Lex/HeaderSearch.h

HeaderFileInfo()
       : isImport(false), isPragmaOnce(false), DirInfo(SrcMgr::C_User),
         External(false), isModuleHeader(false), isCompilingModuleHeader(false),
         Resolved(false), IndexHeaderMapHeader(false), IsValid(false)  {}
 
   /// Retrieve the controlling macro for this header file, if
   /// any.
   const IdentifierInfo *
   getControllingMacro(ExternalPreprocessorSource *External);
-
-  /// Determine whether this is a non-default header file info, e.g.,
-  /// it corresponds to an actual header we've included or tried to include.
-  bool isNonDefault() const {
-    return isImport || isPragmaOnce || NumIncludes || ControllingMacro ||
-      ControllingMacroID;
-  }
 };
 
 /// An external source of header file information, which may supply
 /// information about header files already included.
 class ExternalHeaderFileInfoSource {
 public:
   virtual ~ExternalHeaderFileInfoSource();