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/0652-Optimize-entity-tracker-passenger-checks.patch

@@ -1,19 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Andrew Steinborn <git@steinborn.me>
-Date: Sun, 8 Aug 2021 00:52:54 -0400
-Subject: [PATCH] Optimize entity tracker passenger checks
-
-
-diff --git a/src/main/java/net/minecraft/server/level/ServerEntity.java b/src/main/java/net/minecraft/server/level/ServerEntity.java
-index 3f3c7ced3a43e2b0eb451930c09188e3706a1bee..3a7a0e24e1c12ae044a455ee4f85216508e97d21 100644
---- a/src/main/java/net/minecraft/server/level/ServerEntity.java
-+++ b/src/main/java/net/minecraft/server/level/ServerEntity.java
-@@ -76,7 +76,7 @@ public class ServerEntity {
-         this.trackedPlayers = trackedPlayers;
-         // CraftBukkit end
-         this.ap = Vec3.ZERO;
--        this.lastPassengers = Collections.emptyList();
-+        this.lastPassengers = com.google.common.collect.ImmutableList.of(); // Paper - optimize passenger checks
-         this.level = worldserver;
-         this.broadcast = consumer;
-         this.entity = entity;