system: add disk usage task

src/taskworker.js

@@ -16,7 +16,6 @@ const apptask = require('./apptask.js'),
     net = require('net'),
     reverseProxy = require('./reverseproxy.js'),
     safe = require('safetydance'),
-    system = require('./system.js'),
     tasks = require('./tasks.js'),
     updater = require('./updater.js');
 
@@ -31,7 +30,6 @@ const TASKS = { // indexed by task type
     changeMailLocation: mailServer.changeLocation,
     syncDnsRecords: dns.syncDnsRecords,
     syncDyndns: dyndns.sync,
-    updateDiskUsage: system.updateDiskUsage,
 
     _identity: async (arg, progressCallback) => { progressCallback({ percent: 20 }); return arg; },
     _error: async (arg, progressCallback) => { progressCallback({ percent: 20 }); throw new Error(`Failed for arg: ${arg}`); },