purge: move extension into core mercurial The motivation is simple: it's nicer to avoid gating basic functionality. To reduce the risk of people shooting themselves in the feet, `--confirm` is now the default, unless the extensions is loaded.. For review of the body of the purge command, use this instead of what hg/phabricator will show (the block of code is modified, not just moved): Differential Revision: https://phab.mercurial-scm.org/D9820