remove unused ioredis package

it is loaded from redis-sharelatex, not here.

services/document-updater/package.json

@@ -10,7 +10,6 @@
     "async": "^2.5.0",
     "coffee-script": "1.4.0",
     "express": "3.3.4",
-    "ioredis": "^3.1.4",
     "logger-sharelatex": "git+https://github.com/sharelatex/logger-sharelatex.git#v1.5.6",
     "lynx": "0.0.11",
     "metrics-sharelatex": "git+https://github.com/sharelatex/metrics-sharelatex.git#v1.5.0",