GAZIANTEP, Turkey — Turkey’s prime minister said Saturday the number of migrants crossing into Greece illegally has dropped considerably, as proof that a much criticized migration deal between Turkey and the European Union is working. Ahmet Davutolgu was speaking at a joint news conference with German Chancellor Angela Merkel and top European Union officials who traveled near Turkey’s border with Syria in a bid to promote the troubled deal with Turkey as they face increasing pressure to reassess the agreement. The group toured a refugee camp and inaugurated a child support center funded by the EU. European Union Council President Donald Tusk said the EU plans to spend 1 billion euros ($1.1...