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/0097-Async-GameProfileCache-saving.patch

@@ -5,10 +5,10 @@ Subject: [PATCH] Async GameProfileCache saving
 
 
 diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
-index d8f2fe077e35fd6c70e0ba50945006819f50586f..d566d64c6c3bd97ac4b4f80bdf1b1bd5a381ef55 100644
+index f16ade2019e58a9374a550f58113313c118c2f2b..10d69b48158460e5739d1e41a83fcaeec819fac6 100644
 --- a/src/main/java/net/minecraft/server/MinecraftServer.java
 +++ b/src/main/java/net/minecraft/server/MinecraftServer.java
-@@ -999,7 +999,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
+@@ -998,7 +998,7 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
          } catch (java.lang.InterruptedException ignored) {} // Paper
          if (org.spigotmc.SpigotConfig.saveUserCacheOnStopOnly) {
              MinecraftServer.LOGGER.info("Saving usercache.json");