#1396 Remove an unneeded include (which was moreover triggering a warning as...

#1396 Remove an unneeded include (which was moreover triggering a warning as it was in experimental directory).

Sources/Operators/LocalVariationalOperator/Internal/ElementaryDataImpl.hpp

@@ -19,7 +19,6 @@
 # include <vector>
 # include <array>
 # include <cassert>
-# include <experimental/optional>
 
 # include "Utilities/Pragma/Pragma.hpp"
 # include "Utilities/Optional.hpp"