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/All-chunks-are-slime-spawn-chunks-toggle.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] All chunks are slime spawn chunks toggle
 
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 2782970393..be91b11242 100644
+index e80ffe34a..95245a981 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 2782970393..be91b11242 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/EntitySlime.java b/src/main/java/net/minecraft/server/EntitySlime.java
-index c3d4d00483..039050f634 100644
+index 87c37c0d6..a5238c673 100644
 --- a/src/main/java/net/minecraft/server/EntitySlime.java
 +++ b/src/main/java/net/minecraft/server/EntitySlime.java
 @@ -0,0 +0,0 @@ public class EntitySlime extends EntityInsentient implements IMonster {