Foreigners snapping up private apartments in Singapore declined to a 17-year low in 2020 as travel restrictions and lockdowns in various countries deterred them from coming to the city state.Purchases of units fell to 742 last year, according to Singapore-based real estate consultancy firms ERA Realty Network and OrangeTee & Tie Pte. That is the lowest since 2003, when non-permanent residents bought 671 units, based on an analysis of government data as of Tuesday that takes into account new,…