obsdiscovery: extract push-obshashtree discovery in a function This will help use to simplify the code.

obsdiscovery: directly use the 'only' revset for obshashtree The revset now exists and is fast. This remove the needs to hold a reference to "revs" in that code.

obsdiscovery: extract push-obshashrange discovery in a function This will help us to simplify the code. The code is updated to directly use 'outgoing' missing so that is no longer needs to access 'futureheads'.

obsdiscovery: merge two distinct if statement It did not made any sense for them to be split.