sql server doesn't accept to insert a blank datetime like `0001-01-01 00:00:00`. So that we have a break change here that deleted column should not have a notnull tag.
Reviewed-on: https://gitea.com/xorm/xorm/pulls/1936
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-committed-by: Lunny Xiao <xiaolunwen@gmail.com>