core: consider removing the LocalPrivateKey method from secure connections

[Stebalien]

It's really not necessary and generally not a good idea to expose private keys like this.

[whyrusleeping]

To clarify this scary sounding issue, @Stebalien is talking about the LocalPrivateKey method on the secureConn type that returns the private key we are using for the encrypted channel. Its not (as one might assume by reading the title) leaking private key data over the network in any way.