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/0813-WorldCreator-keepSpawnLoaded.patch

@@ -1,18 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Shane Freeder <theboyetronic@gmail.com>
-Date: Sat, 3 Jul 2021 21:18:28 +0100
-Subject: [PATCH] WorldCreator#keepSpawnLoaded
-
-
-diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
-index c020acc1bcfe3471728c143862625463d7c82dd8..cabb66678afdad83341dd3b1a662cadeef4a4196 100644
---- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
-+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
-@@ -1272,6 +1272,7 @@ public final class CraftServer implements Server {
-         internal.setSpawnSettings(true, true);
-         // Paper - move up
- 
-+        internal.keepSpawnInMemory = creator.keepSpawnLoaded().toBooleanOrElse(internal.getWorld().getKeepSpawnInMemory()); // Paper
-         this.getServer().prepareLevels(internal.getChunkSource().chunkMap.progressListener, internal);
-         //internal.entityManager.tick(); // SPIGOT-6526: Load pending entities so they are available to the API // Paper - rewrite chunk system
-