Remove instruction to create multiple private networks to peer the same VPC.

In AWS it is possible to associate multiple CIDR to a single VPC. In our docs we suggest creating multiple private networks, one for each of the CIDR, for this use case.

 If you have multiple CIDR blocks associated with a VPC you will need to set up multiple private networks, one for each CIDR block. 

This does not work and we should remove the suggestion. Aside from untested workarounds (like using CIDR that subsume all of the CIDR associated with the VPC) we do not seem to support private networking with such VPCs at this time.