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/0302-Prevent-bees-loading-chunks-checking-hive-position.patch

@@ -0,0 +1,18 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: William Blake Galbreath <Blake.Galbreath@GMail.com>
+Date: Sun, 5 Jan 2020 17:24:34 -0600
+Subject: [PATCH] Prevent bees loading chunks checking hive position
+
+
+diff --git a/src/main/java/net/minecraft/world/entity/animal/Bee.java b/src/main/java/net/minecraft/world/entity/animal/Bee.java
+index 048d03c8ef3ef865641b2276477cf84e8d4397a1..58536ee8707c5ad0625cae2f26a58cf03b3f85d7 100644
+--- a/src/main/java/net/minecraft/world/entity/animal/Bee.java
++++ b/src/main/java/net/minecraft/world/entity/animal/Bee.java
+@@ -510,6 +510,7 @@ public class Bee extends Animal implements NeutralMob, FlyingAnimal {
+         } else if (this.isTooFarAway(this.hivePos)) {
+             return false;
+         } else {
++            if (this.level().getChunkIfLoadedImmediately(this.hivePos.getX() >> 4, this.hivePos.getZ() >> 4) == null) return true; // Paper - just assume the hive is still there, no need to load the chunk(s)
+             BlockEntity tileentity = this.level().getBlockEntity(this.hivePos);
+ 
+             return tileentity != null && tileentity.getType() == BlockEntityType.BEEHIVE;