Remove Discord mentions

We're transitioning to https://community.apollographql.com/

Author: martinbonnin

README.md

@@ -6,7 +6,6 @@
 
 [![Discourse](https://img.shields.io/discourse/topics?label=Discourse&server=https%3A%2F%2Fcommunity.apollographql.com&logo=discourse&color=467B95&style=flat-square)](http://community.apollographql.com/new-topic?category=Help&tags=mobile,client)
 [![Slack](https://img.shields.io/static/v1?label=kotlinlang&message=apollo-kotlin&color=A97BFF&logo=slack&style=flat-square)](https://app.slack.com/client/T09229ZC6/C01A6KM1SBZ)
-[![Discord](https://img.shields.io/discord/1022972389463687228.svg?color=7389D8&labelColor=6A7EC2&logo=discord&logoColor=ffffff&style=flat-square)](https://discord.com/invite/graphos)
 
 [![Maven Central](https://img.shields.io/maven-central/v/com.apollographql.execution/apollo-execution-runtime?style=flat-square)](https://central.sonatype.com/namespace/com.apollographql.execution)
 [![OSS Snapshots](https://img.shields.io/nexus/s/com.apollographql.execution/apollo-execution-runtime?server=https%3A%2F%2Fs01.oss.sonatype.org&label=oss-snapshots&style=flat-square)](https://s01.oss.sonatype.org/content/repositories/snapshots/com/apollographql/execution/)