Adds delete difficulty option to editor

osu.Game/Screens/Edit/Editor.cs

@@ -849,6 +849,20 @@ namespace osu.Game.Screens.Edit
             new LegacyBeatmapExporter(storage).Export(Beatmap.Value.BeatmapSetInfo);
         }
 
+        private void deleteDifficulty()
+        {
+            dialogOverlay?.Push(new PromptForDifficultyDeleteDialog(confirmDifficultyDelete, () => { }));
+        }
+
+        private void confirmDifficultyDelete()
+        {
+            var current = playableBeatmap.BeatmapInfo;
+            if (current is null) return;
+
+            beatmapManager.Hide(current);
+            this.Exit();
+        }
+
         private void updateLastSavedHash()
         {
             lastSavedHash = changeHandler?.CurrentStateHash;
@@ -869,6 +883,10 @@ namespace osu.Game.Screens.Edit
             fileMenuItems.Add(createDifficultyCreationMenu());
             fileMenuItems.Add(createDifficultySwitchMenu());
 
+            fileMenuItems.Add(new EditorMenuItemSpacer());
+
+            fileMenuItems.Add(new EditorMenuItem("Delete difficulty", MenuItemType.Standard, deleteDifficulty));
+
             fileMenuItems.Add(new EditorMenuItemSpacer());
             fileMenuItems.Add(new EditorMenuItem("Exit", MenuItemType.Standard, this.Exit));
             return fileMenuItems;

osu.Game/Screens/Edit/PromptForDifficultyDeleteDialog.cs

@@ -0,0 +1,33 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Framework.Graphics.Sprites;
+using osu.Game.Overlays.Dialog;
+
+namespace osu.Game.Screens.Edit
+{
+    public class PromptForDifficultyDeleteDialog : PopupDialog
+    {
+        public PromptForDifficultyDeleteDialog(Action delete, Action cancel)
+        {
+            HeaderText = "Are you sure you want to delete this difficulty?";
+
+            Icon = FontAwesome.Regular.Save;
+
+            Buttons = new PopupDialogButton[]
+            {
+                new PopupDialogDangerousButton
+                {
+                    Text = @"Yes delete this difficulty!",
+                    Action = delete
+                },
+                new PopupDialogCancelButton
+                {
+                    Text = @"Oops, continue editing",
+                    Action = cancel
+                },
+            };
+        }
+    }
+}