unfollowUser method
Implementation
void unfollowUser(String userId) async {
final result = await friendshipManager.unfollowUser(userIDList: [userId]);
const success = 0;
if (result.code == success) {
final Set<String> followingList = Set.from(state.followingList.value);
followingList.removeWhere((userID) => userID == userId);
state.followingList.value = followingList;
getFansNumber();
}
}