remove node net module

[heapwolf]

After we get the new utp module done, we should remove net module to reduce size/complexity. It's only used in a few places.

%grep "require('net" -R . 
./node_modules/bind-easy/test.js:const net = require('net')
./node_modules/bind-easy/index.js:const net = require('net')
./node_modules/@hyperswarm/dht/test/connections.js:const net = require('net')
./node_modules/@hyperswarm/dht/lib/socket-pairer.js:const net = require('net')
./node_modules/@hyperswarm/secret-stream/test.js:const net = require('net')

[kasperisager]

I plan on tackling this in #82.

[mafintosh]

in master