net: use std::chrono throughout maxOutbound logic

Summary:

Switch to using std::chrono types for the max outbound related logic.
Removes some unnecessary code from init.

Backport of core#20253.

Depends on D10901.

Ref T1696.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1696

Differential Revision: https://reviews.bitcoinabc.org/D10902