[avalanche] Let -maxavalancheoutbound takes precedence over -maxconnections

Summary: And remove the -maxconnections option from the example config file. This options has led to several issues for avalanche users using it as a habit.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Subscribers: PiRK

Differential Revision: https://reviews.bitcoinabc.org/D14969