Clear the wordpress-rs cache on logout and site removal #23240

wordpress-rs exposes removeSelfHostedSite and removeWordpressComSite, which delete a site and its cached rows. Neither is called anywhere in this repo.

Site removal currently goes through FluxC SiteAction.REMOVE_SITE, which does not touch wordpress-rs. Logout calls wpServiceProvider.clearAll() (AppInitializer.kt:722), which is services.clear() on an in-memory map (WpServiceProvider.kt:47-49) and leaves the database file untouched.

Worth investigating whether we should call these APIs on logout and site removal.

Note that this requires wordpress-rs:0.7.0 update in #23237 to land first.