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-mob-spawner-tick-rate.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Configurable mob spawner tick rate
 
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 8db5c3f3fe..e4e00e2e1c 100644
+index 77444bb90..2e9bbc7e9 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 {
@@ -19,7 +19,7 @@ index 8db5c3f3fe..e4e00e2e1c 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
-index a2140cb6c5..b3af4ba233 100644
+index dc0e93926..13e62e3d7 100644
 --- a/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
 +++ b/src/main/java/net/minecraft/server/MobSpawnerAbstract.java
 @@ -0,0 +0,0 @@ public abstract class MobSpawnerAbstract {