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/0501-Add-fast-alternative-constructor-for-Rotations.patch

@@ -0,0 +1,29 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Irmo van den Berge <irmo.vandenberge@ziggo.nl>
+Date: Wed, 10 Mar 2021 21:26:31 +0100
+Subject: [PATCH] Add fast alternative constructor for Rotations
+
+
+diff --git a/src/main/java/net/minecraft/core/Rotations.java b/src/main/java/net/minecraft/core/Rotations.java
+index e6c97efb3aa89646149d11bb0ae4420b3977d214..27007280dba9e6d19a50dc2a4b160e96b20c67f7 100644
+--- a/src/main/java/net/minecraft/core/Rotations.java
++++ b/src/main/java/net/minecraft/core/Rotations.java
+@@ -34,6 +34,18 @@ public class Rotations {
+         this(serialized.getFloat(0), serialized.getFloat(1), serialized.getFloat(2));
+     }
+ 
++    // Paper start - faster alternative constructor
++    private Rotations(float x, float y, float z, Void dummy_var) {
++        this.x = x;
++        this.y = y;
++        this.z = z;
++    }
++
++    public static Rotations createWithoutValidityChecks(float x, float y, float z) {
++        return new Rotations(x, y, z, null);
++    }
++    // Paper end - faster alternative constructor
++
+     public ListTag save() {
+         ListTag listTag = new ListTag();
+         listTag.add(FloatTag.valueOf(this.x));