cmTarget: Split storage of link implementation from backtraces.

Source/cmListFileCache.h

@@ -111,13 +111,4 @@ struct cmListFile
   std::vector<cmListFileFunction> Functions;
 };
 
-struct cmValueWithOrigin {
-  cmValueWithOrigin(const std::string &value,
-                          const cmListFileBacktrace &bt)
-    : Value(value), Backtrace(bt)
-  {}
-  std::string Value;
-  cmListFileBacktrace Backtrace;
-};
-
 #endif