Add Virtual Destructor to SimpleTable

The TableContainer manages pointers to types derived from this base
class so for orderly destruction we really should have virtual
destructors here.

opm/input/eclipse/EclipseState/Tables/SimpleTable.hpp

@@ -39,6 +39,8 @@ namespace Opm {
         SimpleTable(TableSchema, const std::string& tableName, const DeckItem& deckItem, const int tableID);
         explicit SimpleTable( TableSchema );
 
+        virtual ~SimpleTable() = default;
+
         static SimpleTable serializationTestObject();
 
         void addColumns();