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/0498-Add-Block-isValidTool.patch

@@ -0,0 +1,20 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jake Potrebic <jake.m.potrebic@gmail.com>
+Date: Mon, 6 Jul 2020 12:44:31 -0700
+Subject: [PATCH] Add Block#isValidTool
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java b/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
+index 98e87dc15e2ed23f6897ba6359846ff5bc32b655..2034858a53c4c887da334cdc7713997daa01124f 100644
+--- a/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
++++ b/src/main/java/org/bukkit/craftbukkit/block/CraftBlock.java
+@@ -693,5 +693,9 @@ public class CraftBlock implements Block {
+     public String translationKey() {
+         return this.getNMS().getBlock().getDescriptionId();
+     }
++
++    public boolean isValidTool(ItemStack itemStack) {
++        return getDrops(itemStack).size() != 0;
++    }
+     // Paper end
+ }