No using namespace in include (AliceO2Group#4438)

Author: aphecetche

Analysis/Core/include/Analysis/HistogramManager.h

@@ -28,8 +28,6 @@
 #include <vector>
 #include <list>
 
-using namespace std;
-
 class HistogramManager : public TNamed
 {
 
@@ -96,8 +94,8 @@ class HistogramManager : public TNamed
   void Print(Option_t*) const override;
 
  private:
-  THashList* fMainList;                                             // master histogram list
-  int fNVars;                                                       // number of variables handled (tipically from the Variable Manager)
+  THashList* fMainList; // master histogram list
+  int fNVars;           // number of variables handled (tipically from the Variable Manager)
 
   bool* fUsedVars;                                                  //! flags of used variables
   std::map<std::string, std::list<std::vector<int>>> fVariablesMap; //!  map holding identifiers for all variables needed by histograms