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/Configurable-spawn-chances-for-skeleton-horses.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Configurable spawn chances for skeleton horses
 
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 98049567f4..2a71381dae 100644
+index b72da38a7..b910b648f 100644
 --- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 @@ -0,0 +0,0 @@ public class PaperWorldConfig {
@@ -22,7 +22,7 @@ index 98049567f4..2a71381dae 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
-index 9928e5aab7..d3039c2fd9 100644
+index 9928e5aab..d3039c2fd 100644
 --- a/src/main/java/net/minecraft/server/WorldServer.java
 +++ b/src/main/java/net/minecraft/server/WorldServer.java
 @@ -0,0 +0,0 @@ public class WorldServer extends World {