Code format via ./gradlew :firebase-firestore:googleJavaFormat

Author: dconeybe

firebase-firestore/src/main/java/com/google/firebase/firestore/core/SyncEngine.java

@@ -57,7 +57,6 @@
 import com.google.firebase.firestore.util.Util;
 import io.grpc.Status;
 import java.io.IOException;
-import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;