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/0602-Add-environment-variable-to-disable-server-gui.patch

@@ -1,18 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Riley Park <rileysebastianpark@gmail.com>
-Date: Mon, 17 May 2021 00:34:55 -0700
-Subject: [PATCH] Add environment variable to disable server gui
-
-
-diff --git a/src/main/java/net/minecraft/server/Main.java b/src/main/java/net/minecraft/server/Main.java
-index cac1ef2fefc2e3f2dde820b71a23e72a8a5f3fd7..98385550084c9f975e494668961bac6ccb0700ab 100644
---- a/src/main/java/net/minecraft/server/Main.java
-+++ b/src/main/java/net/minecraft/server/Main.java
-@@ -293,6 +293,7 @@ public class Main {
-                 */
-                 boolean flag1 = !optionset.has("nogui") && !optionset.nonOptionArguments().contains("nogui");
- 
-+                if(!Boolean.parseBoolean(System.getenv().getOrDefault("PAPER_DISABLE_SERVER_GUI", String.valueOf(false)))) // Paper
-                 if (flag1 && !GraphicsEnvironment.isHeadless()) {
-                     dedicatedserver1.showGui();
-                 }