remove unused class Unit

Param/Base/Unit.h

-//  ************************************************************************************************
-//
-//  BornAgain: simulate and fit reflection and scattering
-//
-//! @file      Param/Base/Unit.h
-//! @brief     Defines class Unit.
-//!
-//! @homepage  http://www.bornagainproject.org
-//! @license   GNU General Public License v3 or higher (see COPYING)
-//! @copyright Forschungszentrum Jülich GmbH 2018
-//! @authors   Scientific Computing Group at MLZ (see CITATION, AUTHORS)
-//
-//  ************************************************************************************************
-
-#ifdef SWIG
-#error no need to expose this header to Swig
-#endif
-
-#ifndef USER_API
-#ifndef BORNAGAIN_PARAM_BASE_UNIT_H
-#define BORNAGAIN_PARAM_BASE_UNIT_H
-
-#include <string>
-
-//! A physical unit.
-
-class Unit {
-public:
-    explicit Unit(const std::string& name = "") : m_name(name) {}
-    void setUnit(const std::string& name) { m_name = name; }
-    const std::string& getName() const { return m_name; }
-
-private:
-    std::string m_name;
-};
-
-#endif // BORNAGAIN_PARAM_BASE_UNIT_H
-#endif // USER_API