Do not store the dimension registry for each connected server

This was unused and did little more than add unnecessary memory usage. The only time we need the dimension registry is during server switching - once that is done, we no longer need the registry.

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/VelocityServerConnection.java

@@ -53,8 +53,6 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
-import net.kyori.adventure.nbt.CompoundBinaryTag;
-import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.jetbrains.annotations.NotNull;
 
@@ -72,7 +70,6 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
   private boolean gracefulDisconnect = false;
   private BackendConnectionPhase connectionPhase = BackendConnectionPhases.UNKNOWN;
   private final Map<Long, Long> pendingPings = new HashMap<>();
-  private @MonotonicNonNull CompoundBinaryTag activeDimensionRegistry;
 
   /**
    * Initializes a new server connection.
@@ -366,12 +363,4 @@ public class VelocityServerConnection implements MinecraftConnectionAssociation,
   public boolean hasCompletedJoin() {
     return hasCompletedJoin;
   }
-
-  public CompoundBinaryTag getActiveDimensionRegistry() {
-    return activeDimensionRegistry;
-  }
-
-  public void setActiveDimensionRegistry(CompoundBinaryTag activeDimensionRegistry) {
-    this.activeDimensionRegistry = activeDimensionRegistry;
-  }
 }

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -565,8 +565,6 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
       }
     }
 
-    destination.setActiveDimensionRegistry(joinGame.getRegistry()); // 1.16
-
     // Remove previous boss bars. These don't get cleared when sending JoinGame, thus the need to
     // track them.
     for (UUID serverBossBar : serverBossBars) {