Get rid of strong pillar dependency

[krlmlr]

Make it optional, to reduce dependencies of RSQLite and other database packages: http://dirk.eddelbuettel.com/blog/2018/02/28/#017_dependencies. Same technique as used for hms.

Thanks @eddelbuettel!

[github-actions]

This old thread has been automatically locked. If you think you have found something related to this, please open a new issue and link to this old issue if necessary.