Fix error handler returning two responses

The error handler mistakenly sent two responses on error, the first
being a 200.

services/filestore/app/js/RequestLogger.js

@@ -17,10 +17,7 @@ class RequestLogger {
 
   static errorHandler(err, req, res, next) {
     req.requestLogger.addFields({ error: err })
-    res
+    res.status(500).send(err.message)
-      .send(err.message)
-      .status(500)
-      .end()
   }
 
   static middleware(req, res, next) {