Revert "Fix FOUC with inject CSS files"

This reverts commit eeb661b6cd.

This was causing CSS to pile up over and over each time javascript did an HTTP request, which resulted in massive slowdown over time.

app/src/components/mainWindow/mainWindow.js

@@ -125,7 +125,7 @@ function createMainWindow(options, onAppQuit, setDockBadge) {
         mainWindow.webContents.setUserAgent(options.userAgent);
     }
 
-    mainWindow.webContents.on('did-get-response-details', () => {
+    mainWindow.webContents.on('did-finish-load', () => {
         mainWindow.webContents.send('params', JSON.stringify(options));
         mainWindow.webContents.insertCSS(getCssToInject());
     });