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/0617-Don-t-log-debug-logging-being-disabled.patch

@@ -0,0 +1,19 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Noah van der Aa <ndvdaa@gmail.com>
+Date: Tue, 14 Sep 2021 16:24:45 +0200
+Subject: [PATCH] Don't log debug logging being disabled
+
+
+diff --git a/src/main/java/org/spigotmc/SpigotConfig.java b/src/main/java/org/spigotmc/SpigotConfig.java
+index 85f3433860abd91a89961907940a807a8b190a46..4dbb109d0526afee99b9190fc256585121aac9b5 100644
+--- a/src/main/java/org/spigotmc/SpigotConfig.java
++++ b/src/main/java/org/spigotmc/SpigotConfig.java
+@@ -381,7 +381,7 @@ public class SpigotConfig
+             Bukkit.getLogger().info( "Debug logging is enabled" );
+         } else
+         {
+-            Bukkit.getLogger().info( "Debug logging is disabled" );
++            // Bukkit.getLogger().info( "Debug logging is disabled" ); // Paper - Don't log if debug logging isn't enabled.
+         }
+     }
+