Drop hardcoded 'connection: local' in playbook so it can be configured in inventory

[geerlingguy]

I was talking with Jeff Vincent from MacStadium.com, and he likes to demo using this playbook to manage cloud Mac servers—and it would be super easy to make it easier to manage other machines by just dropping this line: https://github.com/geerlingguy/mac-dev-playbook/blob/master/main.yml#L3

Instead, that connection option can be in the inventory, and I could add in the README how to configure the inventory for remote server administration (vs. the default of running on the local host).

See https://docs.macstadium.com/docs/ansible