dgram: remove unreachable connectState assign

isConnected() returns true implies that remoteAddress() doesn't throw an error. The implementation of remoteAddress is as follows:

https://github.com/nodejs/node/blob/29f1b609ba5d12d3903379bb72ff5aa6e6225568/lib/dgram.js#L770-L775

It also implies that state.connectState === CONNECT_STATE_CONNECTED.

So it seems not necessary to assign it again.