gtk4: Merge "present" and "supported" versions of right_..._unit_release()
middle_..._unit_release() ones have the difference that "supported" units one closes city dialog of the unit home city, "present" one city dialog of the city on the unit tile.
gtk4-client (maybe also gtk3.22-client?) right_..._unit_release() functions for supported and present units seem identical. Merge them.