Package.json: remove "private": false field

This field is being removed by Yarn 2+ (`"private": true` stays untouched). This commit basically offloads this PR: adeira/universe#2154

adeira-source-id: 2e06a4b2c37428ed66406781dea2d76e6200fed7

package.json

@@ -1,6 +1,5 @@
 {
   "name": "@adeira/graphql-relay",
-  "private": false,
   "sideEffects": false,
   "version": "0.3.0",
   "description": "A library to help construct a graphql-js server supporting react-relay.",