[CI-SKIP] Drop Allow PlayerEditBookEvent to fire for off hand (#5471)

Upstream fixed this in a different way (using -1 for off hand instead of the real slot id...) so this patch is no longer needed.

Spigot-API-Patches/0284-Allow-PlayerEditBookEvent-to-fire-for-off-hand.patch

@@ -1,19 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: jmp <jasonpenilla2@me.com>
-Date: Mon, 5 Apr 2021 18:35:37 -0700
-Subject: [PATCH] Allow PlayerEditBookEvent to fire for off hand
-
-
-diff --git a/src/main/java/org/bukkit/event/player/PlayerEditBookEvent.java b/src/main/java/org/bukkit/event/player/PlayerEditBookEvent.java
-index c8fda418bd5e0e6c299900be469862dbc5d7a56f..b8994a6d023c124f2c068d2e69f2c3d949b9405e 100644
---- a/src/main/java/org/bukkit/event/player/PlayerEditBookEvent.java
-+++ b/src/main/java/org/bukkit/event/player/PlayerEditBookEvent.java
-@@ -24,7 +24,7 @@ public class PlayerEditBookEvent extends PlayerEvent implements Cancellable {
-     public PlayerEditBookEvent(@NotNull Player who, int slot, @NotNull BookMeta previousBookMeta, @NotNull BookMeta newBookMeta, boolean isSigning) {
-         super(who);
- 
--        Validate.isTrue(slot >= -1 && slot <= 8, "Slot must be in range (-1)-8 inclusive");
-+        Validate.isTrue(slot == 40 || slot >= -1 && slot <= 8, "Slot must be in range (-1)-8 inclusive"); // Paper - off hand is 40
-         Validate.notNull(previousBookMeta, "Previous book meta must not be null");
-         Validate.notNull(newBookMeta, "New book meta must not be null");
-