Remove call to Render()

As far as I can tell, this is not needed. The call to Refresh at the end of
backgroundFetch takes care of redrawing after refreshing.

The call was added in 2fc1498517, that's a long time ago, and we had multiple
big refactorings since then. Maybe it was needed back then but no longer is
today.

pkg/gui/background.go

@@ -76,9 +76,7 @@ func (self *BackgroundRoutineMgr) startBackgroundFetch() {
 	self.gui.waitForIntro.Wait()
 
 	fetch := func() error {
-		err := self.backgroundFetch()
-		self.gui.c.Render()
-		return err
+		return self.backgroundFetch()
 	}
 
 	// We want an immediate fetch at startup, and since goEvery starts by