Fully remove scarpet commands when apps are unloaded (#1452)

Using new Loader 0.14+ features

src/main/java/carpet/mixins/CommandNode_scarpetCommandsMixin.java

@@ -0,0 +1,30 @@
+package carpet.mixins;
+
+import java.util.Map;
+
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+
+import com.mojang.brigadier.tree.ArgumentCommandNode;
+import com.mojang.brigadier.tree.CommandNode;
+import com.mojang.brigadier.tree.LiteralCommandNode;
+
+import carpet.fakes.CommandNodeInterface;
+
+@Mixin(CommandNode.class)
+public class CommandNode_scarpetCommandsMixin<S> implements CommandNodeInterface {
+    @Shadow @Final
+    private Map<String, CommandNode<S>> children;
+    @Shadow @Final
+    private Map<String, LiteralCommandNode<S>> literals;
+    @Shadow @Final
+    private Map<String, ArgumentCommandNode<S, ?>> arguments;
+    
+    @Override
+    public void carpet$removeChild(String name) {
+        this.children.remove(name);
+        this.literals.remove(name);
+        this.arguments.remove(name);
+    }
+}