Inventory: remove a bunch of crap from interface

some of these (notably the on* methods) are internal and shouldn't be exposed via interface (same crap as Plugin->onEnable() onDisable() etc) and the rest of the stuff is entirely unused.

src/pocketmine/inventory/PlayerInventory.php

@@ -48,10 +48,6 @@ class PlayerInventory extends BaseInventory{
 		parent::__construct();
 	}
 
-	public function getName() : string{
-		return "Player";
-	}
-
 	public function getDefaultSize() : int{
 		return 36;
 	}