Stop filtering remove-entity packets in TechHider

Stripping ids of hidden entities left ghost entities on clients once
the entity became visible and was later removed. Removing an unknown
entity id is harmless, so the packet is passed through.

SpigotCore/SpigotCore_Main/src/de/steamwar/techhider/TechHider.java

@@ -182,6 +182,9 @@ public class TechHider {
                 ClientboundSetChunkCacheCenterPacket.class, // 7.1.93 Set Center Chunk
                 ClientboundForgetLevelChunkPacket.class, // 7.1.38 Unload Chunk
                 ClientboundUpdateTagsPacket.class, // 7.1.133 Update Tags (play)
+                // 7.1.76 Remove Entities: must not be filtered, otherwise Player#hideEntity leaves ghosts on the client.
+                // Entities that are already gone from the world pass the entity checks anyway, so no additional information is leaked.
+                ClientboundRemoveEntitiesPacket.class,
                 ClientboundPlayerInfoRemovePacket.class, // 7.1.68 Player Info Remove
                 ClientboundPlayerInfoUpdatePacket.class, // 7.1.69 Player Info Update
                 ClientboundMoveVehiclePacket.class, // 7.1.56 Move Vehicle (vehicle the player is in)
@@ -242,8 +245,6 @@ public class TechHider {
 
         // 7.1.82 Set Head Rotation: entity id and rotation.
         processors.put(ClientboundRotateHeadPacket.class, (access, packet) -> this.processRotateHeadPacket(access, (ClientboundRotateHeadPacket) packet));
-        // 7.1.76 Remove Entities: entity id visibility side channel.
-        processors.put(ClientboundRemoveEntitiesPacket.class, (access, packet) -> this.processRemoveEntitiesPacket(access, (ClientboundRemoveEntitiesPacket) packet));
         // 7.1.99 Link Entities: entity relationship signal.
         processors.put(ClientboundSetEntityLinkPacket.class, (access, packet) -> this.processSetEntityLinkPacket(access, (ClientboundSetEntityLinkPacket) packet));
 
@@ -402,14 +403,6 @@ public class TechHider {
         }
     }
 
-    private Packet<?> processRemoveEntitiesPacket(ForPlayer access, ClientboundRemoveEntitiesPacket packet) {
-        IntList entityIdsToRemove = packet.getEntityIds();
-
-        IntList filteredEntitiesToRemove = entityIdsToRemove.intStream().filter((id) -> access.canAccessEntity(id)).collect(IntArrayList::new, IntList::add, IntList::addAll);
-
-        return new ClientboundRemoveEntitiesPacket(filteredEntitiesToRemove);
-    }
-
     public Packet<?> processSetEntityLinkPacket(ForPlayer access, ClientboundSetEntityLinkPacket packet) {
         int fromEntityId = packet.getSourceId();
         int toEntityId = packet.getDestId();