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/0043-Optimize-explosions.patch

@@ -10,10 +10,10 @@ This patch adds a per-tick cache that is used for storing and retrieving
 an entity's exposure during an explosion.
 
 diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
-index 57ec168bac3727feb734e28cebc680328c1c4aec..4f1204661e345462c08cc66e3a8851033f186268 100644
+index 2f57739431eb695149019724e2923f0d02e88d07..1ba2b1aaf0936963aca73a43632f978c95bf95e6 100644
 --- a/src/main/java/net/minecraft/server/MinecraftServer.java
 +++ b/src/main/java/net/minecraft/server/MinecraftServer.java
-@@ -1573,6 +1573,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
+@@ -1571,6 +1571,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
  
              this.profiler.pop();
              this.profiler.pop();