Remove unused env

Author: nicolelim02

docker-compose-test.yml

@@ -5,8 +5,6 @@ services:
     image: peerprep/user-service
     build: ./backend/user-service
     env_file: ./backend/user-service/.env
-    environment:
-      - MONGO_URI_TEST=mongodb://mongo:mongo@test-mongo:27017/
     depends_on:
       - test-mongo
       - test-redis