feat!: remove a relay immediately instead of unpublishing it

Removing a relay now takes effect immediately:

- the profile stops fetching and advertising it,

- secondary devices immediately apply the removal through the transport sync,

Upgrading removes unpublished relays and triggers keyupdates.

BREAKING CHANGE: set_transport_unpublished() is removed: UIs call delete_transport() when the user removes a relay.

BREAKING CHANGE: list_transports_ex() and the TransportListEntry type are removed: use list_transports().

BREAKING CHANGE: delete_transport() no longer refuses to remove the primary transport: it refuses only to remove the last one and re-elects the sending transport as needed.

BREAKING CHANGE: TransportsModified is now also emitted on the device modifying the transports, not only on devices applying the synced change.

Deprecated: DC_STR_PHASING_OUT

src/sync.rs

@@ -66,8 +66,8 @@ pub(crate) struct TransportData {
     /// Timestamp of when the transport was last time (re)configured.
     pub(crate) timestamp: i64,
 
-    /// Whether the transport is published.
-    /// See [`Context::set_transport_unpublished`] for details.
+    /// Whether the transport is advertised to contacts.
+    /// Always `true` from this core; an older core's `false` is applied as a removal.
     pub(crate) is_published: bool,
 }