DB2 privileged mode is no longer required and should be removed

Currently our DB2Container class uses privileged mode; I think on the basis of this blog post: https://db2indocker.blogspot.com/2015/04/db2-do-not-start-in-un-privileged.html

Kernel 3.15 went EOL in 2014, so this seems like a workaround that shouldn’t be particularly necessary if it’s just for the reason cited in that blog post.

I would suggest that we remove the requirement for privileged mode for the DB2 container, which would mean that none of our modules use privileged mode at all any more. This is ~ better for everybody's security.

Users would still be able to turn on privileged mode for the DB2 container if their kernel made it essential, but I think this is unlikely.

DB2Container クラスがエントリーポイントです。まず、privileged mode の設定を見つけてください。DB2 コンテナが privileged mode なしで起動し、必要な場合にはユーザーが引き続き有効化できることを確認してください。