cleaning: removes redundant api call to Pool.get_all

[GabrielBuica]

With the changes made here, 3ba6e6d, calling Pool.get_all no longer updates the last_active field unless 10 minutes have elapsed since session creation. Therefore, this call should be redundant now.

Passes BVT + BST: 208579 (Dev Run) (except one sequence that hasn't been scheduled)

[robhoes]

See #5986 (comment). This call was there to "correct" the last_active field in case the pool member had a large amount of clock skew with respect to the coordinator. In particular, if the skew is larger than 24 hours, the session may be deleted by the DB GC very quickly. A pretty unusual scenario I suppose...

[edwintorok]

if the skew is larger than 24 hours,

It is a bit odd if the host assigning the session time and the host running db_gc isn't the same one, I would've expected the coordinator to be that one in both cases (well I guess could happen during master promotion, or if this code runs on a member and the members insert the session directly into the DB).

[robhoes]

@edwintorok This is the case particularly for pool members getting their own sessions, i.e. the thing being improved by the session-reuse PR.

[edwintorok]

@edwintorok This is the case particularly for pool members getting their own sessions, i.e. the thing being improved by the session-reuse PR.

If needed we could make the API call only the first time when the session is created, and avoid making the call when we are reusing the session (that one needs some other mechanism of keeping it alive, and I think we will have some mechanism there to avoid destroying those sessions; although we might've temporarily reverted that code)

[GabrielBuica]

I'll move this to draft while we discuss more solutions.