Struktur Arena dan Tindakan Strategis Aktor dalam Pilkada Serentak (Studi Kasus Mundurnya Kandidat Penantang dari Proses Pilkada Kabupaten Timor Tengah Utara Tahun 2015) = The Structure of Arena and The Strategic Action of Actor in Regional Head of Elections (Case Study of Opponents Withdrawal from the 2015 Elections in North Central Timor, Indonesia)