Remove c8y firmware dependency on tedge_timer_ext

Execute the whole firmware operation in a single async method.
 i.e. with no state cached in the actor.

Signed-off-by: Didier Wenzek <didier.wenzek@free.fr>

Author: didier-wenzek

Cargo.lock

@@ -24,7 +24,6 @@ tedge_api = { workspace = true }
 tedge_config = { workspace = true }
 tedge_downloader_ext = { workspace = true }
 tedge_mqtt_ext = { workspace = true }
-tedge_timer_ext = { workspace = true }
 tedge_utils = { workspace = true }
 thiserror = { workspace = true }
 tokio = { workspace = true }