Remove wall-time / unused skip tick protection (#11412)

Spigot still maintains some partial implementation of "tick skipping", a
practice in which the MinecraftServer.currentTick field is updated not
by an increment of one per actual tick, but instead set to
System.currentTimeMillis() / 50. This behaviour means that the tracked
tick may "skip" a tick value in case a previous tick took more than the
expected 50ms.

To compensate for this in important paths, spigot/craftbukkit
implements "wall-time". Instead of incrementing/decrementing ticks on
block entities/entities by one for each call to their tick() method,
they instead increment/decrement important values, like
an ItemEntity's age or pickupDelay, by the difference of
`currentTick - lastTick`, where `lastTick` is the value of
`currentTick` during the last tick() call.

These "fixes" however do not play nicely with minecraft's simulation
distance as entities/block entities implementing the above behaviour
would "catch up" their values when moving from a non-ticking chunk to a
ticking one as their `lastTick` value remains stuck on the last tick in
a ticking chunk and hence lead to a large "catch up" once ticked again.

Paper completely removes the "tick skipping" behaviour (See patch
"Further-improve-server-tick-loop"), making the above precautions
completely unnecessary, which also rids paper of the previous described
incompatibility with non-ticking chunks.

patches/server/0499-Allow-using-signs-inside-spawn-protection.patch

@@ -0,0 +1,20 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Anton Lindroth <ntoonio@gmail.com>
+Date: Wed, 15 Apr 2020 01:54:02 +0200
+Subject: [PATCH] Allow using signs inside spawn protection
+
+
+diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+index d7d36b5148f2e7280816cc70b300b9b10720f751..25d060e8d77b1e8ea2ac951d2b25d60a984398cd 100644
+--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
++++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+@@ -1758,8 +1758,7 @@ public class ServerGamePacketListenerImpl extends ServerCommonPacketListenerImpl
+                     int i = this.player.level().getMaxBuildHeight();
+ 
+                     if (blockposition.getY() < i) {
+-                        if (this.awaitingPositionFromClient == null && worldserver.mayInteract(this.player, blockposition)) {
+-                            this.player.stopUsingItem(); // CraftBukkit - SPIGOT-4706
++                        if (this.awaitingPositionFromClient == null && (worldserver.mayInteract(this.player, blockposition) || (worldserver.paperConfig().spawn.allowUsingSignsInsideSpawnProtection && worldserver.getBlockState(blockposition).getBlock() instanceof net.minecraft.world.level.block.SignBlock))) { // Paper - Allow using signs inside spawn protection
+                             InteractionResult enuminteractionresult = this.player.gameMode.useItemOn(this.player, worldserver, itemstack, enumhand, movingobjectpositionblock);
+ 
+                             if (enuminteractionresult.consumesAction()) {