Remove input_balloon_time setting

This setting doesn't work on most platforms
including some notification daemons on linux.

Where it does work I think it is bad behavior
to default overriding their defaults anyway.

It's most valuable use was likely win32
tray balloons which no longer exist.

src/fe-gtk/notifications/notification-winrt.cpp

@@ -41,7 +41,7 @@ widen(const std::string & to_widen)
 extern "C"
 {
 	__declspec (dllexport) void
-	notification_backend_show (const char *title, const char *text, int timeout)
+	notification_backend_show (const char *title, const char *text)
 	{
 		try
 		{