Fix: Grease Pencil: Missing operator to delete breakdown keyframes

Operation to delete keys generated from interpolate sequence.

Resolves #134081

Pull Request: https://projects.blender.org/blender/blender/pulls/134091

scripts/startup/bl_ui/space_dopesheet.py

@@ -582,6 +582,7 @@ class DOPESHEET_MT_key(Menu):
 
     def draw(self, _context):
         layout = self.layout
+        ob = _context.active_object
 
         layout.menu("DOPESHEET_MT_key_transform", text="Transform")
 
@@ -600,6 +601,8 @@ class DOPESHEET_MT_key(Menu):
         layout.operator("action.paste", text="Paste Flipped").flipped = True
         layout.operator("action.duplicate_move")
         layout.operator("action.delete")
+        if ob and ob.type == 'GREASEPENCIL':
+            layout.operator("grease_pencil.delete_breakdown")
 
         layout.separator()
         layout.operator_menu_enum("action.keyframe_type", "type", text="Keyframe Type")
@@ -785,6 +788,7 @@ class DOPESHEET_MT_context_menu(Menu):
 
         if st.mode == 'GPENCIL':
             layout.separator()
+            layout.operator("grease_pencil.delete_breakdown")
 
         layout.operator_context = 'EXEC_REGION_WIN'
         layout.operator("action.delete")