Connection assumption creates more problems than it solves. It breaks
other features such as bridging.

Connection assumption was there to address the following things. Please
add more in comments if I missed something.

1) Take over wired connections after boot (or after another tool)

NetworkManager should *not* take the wired device down during
initialization. NetworkManager should choose a network connection
configuration and use it to set up the interface. It should
not remove IP addresses only to add them back.

This funcionality should be covered by the normal wired device
startup and doesn't need connection assumption.

2) Keep wired connections up after exit to be taken over later

See bug 683206.

3) Choose the right connection for a wired device after restart

Even though I don't have a use case for this, we already have
a solution. The latest used connection should be always used
unless there's a big reason to choose another (like
interface-specific connection chosen over generic connection).

Administrators will usually make this even easier by using
only one 'autoconnect' connection per interface.