remove "desktop notifications" adv. preference

We move the tooltips to the "mp_alerts_options" window which has
subsumed this preference.

data/advanced_preferences.cfg

@@ -108,14 +108,6 @@
     default=yes
 [/advanced_preference]
 
-[advanced_preference]
-    field=desktop_notifications
-    name= _ "Desktop notifications"
-    description= _ "Shows desktop/system tray notifications for turn change events or conversations when the game window is inactive"
-    type=boolean
-    default=yes
-[/advanced_preference]
-
 [advanced_preference]
     field=flip_time
     name= _ "Reverse time graphics"

data/gui/default/window/mp_alerts_options.cfg

@@ -138,6 +138,7 @@
 									definition = "default"
 
 									label = _ "Play Sound:"
+									tooltip = _ "Play a sound for the event, specified in data/game_config.cfg"
 								[/label]
 							[/column]
 
@@ -153,6 +154,7 @@
 									definition = "default"
 
 									label = _ "Desktop Notification:"
+									tooltip = _ "Shows desktop/system tray notifications for turn change events or conversations when the game window is inactive"
 								[/label]
 							[/column]
 
@@ -167,6 +169,7 @@
 									definition = "default"
 
 									label = _ "Also in main lobby:"
+									tooltip = _ "Also take these actions in response to events in the main multiplayer lobby"
 								[/label]
 							[/column]
 						[/row]

src/desktop/notifications.cpp

@@ -55,8 +55,6 @@ bool available() { return true; }
 
 void send(const std::string& owner, const std::string& message, type t)
 {
-	if (!preferences::get("desktop_notifications", true)) { return; }
-
 	Uint8 app_state = SDL_GetAppState();
 
 	// Do not show notifications when the window is visible...