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

Using new Loader 0.14+ features

src/main/java/carpet/mixins/CommandDispatcher_scarpetCommandsMixin.java

@@ -0,0 +1,22 @@
+package carpet.mixins;
+
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.tree.RootCommandNode;
+
+import carpet.fakes.CommandDispatcherInterface;
+import carpet.fakes.CommandNodeInterface;
+
+@Mixin(CommandDispatcher.class)
+public class CommandDispatcher_scarpetCommandsMixin<S> implements CommandDispatcherInterface {
+    @Shadow @Final
+    private RootCommandNode<S> root;
+
+    @Override
+    public void carpet$unregister(String node) {
+        ((CommandNodeInterface)this.root).carpet$removeChild(node);
+    }
+}