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Upgrading removes unpublished relays and triggers keyupdates.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

docs/schema.sql

@@ -626,13 +626,10 @@ CREATE TABLE transports (
     -- over this table and `removed_transports`, and contacts keep the newest one.
     add_timestamp INTEGER NOT NULL DEFAULT 0,
 
-    -- True if the transport address is published
-    -- by sending it in the public key signature.
+    -- Unused since migration 165, which removed unpublished transports.
     is_published INTEGER DEFAULT 1 NOT NULL,
 
     -- Time when the transport was last used to receive a message.
-    -- Used to remove the least recently used transport
-    -- when a new transport is added and there are too many relays already.
     last_rcvd_timestamp INTEGER NOT NULL DEFAULT 0,
     UNIQUE(addr)
 );