Move missing env var check to index.js

Prevents PR workflow tests throwing as they require the config file. Best to keep ./config.js purely for the config as the checks need only be for starting the bot

Author: mao-sz

config.js

@@ -1,16 +1,5 @@
-const MissingEnvVarError = require('./utils/errors/startup/missing-env-var');
-
 require('dotenv').config();
 
-const missingMandatoryEnvKeys = [
-  'DISCORD_API_KEY',
-  'DISCORD_CLIENT_ID',
-  'DISCORD_GUILD_ID',
-].filter((key) => !process.env[key]);
-if (missingMandatoryEnvKeys.length) {
-  throw new MissingEnvVarError(missingMandatoryEnvKeys);
-}
-
 const config = {
   pointsbot: {
     token: process.env.POINTSBOT_TOKEN,