sound: remove preloading

Sound playing is basically instant -- I was over-engineering when I
added this.

src/renderer/lib/sound.js

@@ -1,5 +1,4 @@
 module.exports = {
-  preload,
   play
 }
 
@@ -47,17 +46,6 @@ const sounds = {
   }
 }
 
-function preload () {
-  for (let name in sounds) {
-    if (!cache[name]) {
-      const sound = sounds[name]
-      const audio = cache[name] = new window.Audio()
-      audio.volume = sound.volume
-      audio.src = sound.url
-    }
-  }
-}
-
 function play (name) {
   let audio = cache[name]
   if (!audio) {

src/renderer/main.js

@@ -132,7 +132,6 @@ function onState (err, _state) {
 // Runs a few seconds after the app loads, to avoid slowing down startup time
 function delayedInit () {
   lazyLoadCast()
-  sound.preload()
 }
 
 // Lazily loads Chromecast and Airplay support