Remove minimum peer error in health check

[sukantoraymond]

Why this should be merged

When setting up private network (e.g. Local Devnet), when there is only 1 validator node, node will remain unhealthy with the message "not connected to a minimum of %d peer(s) only". This PR removes this error message.

How this works

NA

How this was tested

Ran a local Devnet with this version of avalancheGo with 1 Validator only and node passes health check