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/0294-offset-item-frame-ticking.patch

@@ -0,0 +1,19 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: kickash32 <kickash32@gmail.com>
+Date: Tue, 30 Jul 2019 03:17:16 +0500
+Subject: [PATCH] offset item frame ticking
+
+
+diff --git a/src/main/java/net/minecraft/world/entity/decoration/BlockAttachedEntity.java b/src/main/java/net/minecraft/world/entity/decoration/BlockAttachedEntity.java
+index e4eece7bbd14514ec60da26a8744672baa8956f9..7bc612890f941177da11da0ce047d5a74d8ebb33 100644
+--- a/src/main/java/net/minecraft/world/entity/decoration/BlockAttachedEntity.java
++++ b/src/main/java/net/minecraft/world/entity/decoration/BlockAttachedEntity.java
+@@ -26,7 +26,7 @@ import org.bukkit.event.hanging.HangingBreakEvent;
+ public abstract class BlockAttachedEntity extends Entity {
+ 
+     private static final Logger LOGGER = LogUtils.getLogger();
+-    private int checkInterval;
++    private int checkInterval; { this.checkInterval = this.getId() % this.level().spigotConfig.hangingTickFrequency; } // Paper - Perf: offset item frame ticking
+     protected BlockPos pos;
+ 
+     protected BlockAttachedEntity(EntityType<? extends BlockAttachedEntity> type, Level world) {