Remove the GRIST_ALLOWED_HOSTS environment variable (#899)

This mostly reverts commit 49b1749e98.

test/server/lib/helpers/TestServer.ts

@@ -49,7 +49,6 @@ export class TestServer {
       GRIST_PORT: '0',
       GRIST_DISABLE_S3: 'true',
       REDIS_URL: process.env.TEST_REDIS_URL,
-      GRIST_ALLOWED_HOSTS: `example.com,localhost`,
       GRIST_TRIGGER_WAIT_DELAY: '100',
       // this is calculated value, some tests expect 4 attempts and some will try 3 times
       GRIST_TRIGGER_MAX_ATTEMPTS: '4',