Resolve a number of minor warnings (#3495)

src/commands/CmdCalendar.cpp

@@ -177,7 +177,6 @@ int CmdCalendar::execute (std::string& output)
     yFrom = argYear;
 
   // Now begin the data subset and rendering.
-  auto countDueDates = 0;
   if (getPendingDate == true)
   {
     // Find the oldest pending due date.
@@ -190,7 +189,6 @@ int CmdCalendar::execute (std::string& output)
         if (task.has ("due") &&
             !task.hasTag ("nocal"))
         {
-          ++countDueDates;
           Datetime d (task.get ("due"));
           if (d < oldest) oldest = d;
         }

src/commands/CmdCustom.h

@@ -35,7 +35,7 @@ class CmdCustom : public Command
 public:
   CmdCustom (const std::string&, const std::string&, const std::string&);
   bool uses_context () const override;
-  int execute (std::string&);
+  int execute (std::string&) override;
 
 private:
   void validateReportColumns (std::vector <std::string>&);

src/commands/CmdTimesheet.h

@@ -34,7 +34,7 @@ class CmdTimesheet : public Command
 {
 public:
   CmdTimesheet ();
-  int execute (std::string&);
+  int execute (std::string&) override;
   bool uses_context () const override;
 };