Rename baby zombie movement config option

This option does not set the absolute speed of the entity as the name
implies. It sets a modifier. The default (vanilla) value of `0.5` sets
the baby zombie to move at 50% faster than the base speed.

A negative value like `-0.4` would set them to move at 40% slower.

There should be no functional changes as a result of this change, it's
just clarifying the config name.

Spigot-Server-Patches/Optional-TNT-doesn-t-move-in-water.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Optional TNT doesn't move in water
 
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 134c4f7a3..241149c9f 100644
+index 934097163..300cc68a7 100644
 --- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 @@ -0,0 +0,0 @@ package com.destroystokyo.paper;
@@ -32,7 +32,7 @@ index 134c4f7a3..241149c9f 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
-index 47446a74e..2a65a6685 100644
+index 4793bc7d8..0981e9c8c 100644
 --- a/src/main/java/net/minecraft/server/Entity.java
 +++ b/src/main/java/net/minecraft/server/Entity.java
 @@ -0,0 +0,0 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke