server: rest: refactor code to avoid multiple log_response calls

server: rest: refactor code to avoid multiple log_response calls

The 'Ok::<_, Self::Error>(res)' type annotation was from a time where
we could not use async, and had a combinator here which needed
explicity type information. We switched over to async in commit
91e4587343c155cd3aa9274bd2c736dcc1ccf977 and, as the type annotation
is already included in the Future type, we can safely drop it.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>