Drop manual isEditable copy in CraftSign

Signs no longer have a specific isEdiable state, the entire API in this
regard needs updating/deprecation. The boolean field is completely gone,
replaced by a uuid (which will need a new setEditingPlayer(UUID) method
on the Sign interface), and the current upstream implementation of
setEdiable simply flips the is_waxed state.

This patch is hence not needed as it neither allows editing (which will
be redone in a later patch) nor is required to copy the is_waxed boolean
flag as it lives in the signs compound tag and is covered by applyTo.

patches/server/copy-TESign-isEditable-from-snapshots.patch

@@ -1,18 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Shane Freeder <theboyetronic@gmail.com>
-Date: Tue, 23 Mar 2021 06:43:30 +0000
-Subject: [PATCH] copy TESign#isEditable from snapshots
-
-
-diff --git a/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java b/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java
-index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
---- a/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java
-+++ b/src/main/java/org/bukkit/craftbukkit/block/CraftSign.java
-@@ -0,0 +0,0 @@ public class CraftSign<T extends SignBlockEntity> extends CraftBlockEntityState<
-         this.back.applyLegacyStringToSignSide();
- 
-         super.applyTo(sign);
-+        sign.isEditable = getSnapshot().isEditable; // Paper - copy manually
-     }
- 
-     public static void openSign(Sign sign, org.bukkit.entity.HumanEntity player) { // Paper - change move open sign to HumanEntity