import bpy

bl_info = {
    "name": "Delete Default Cube",
    "author": "Your Name",
    "version": (1, 0),
    "blender": (2, 80, 0),
    "location": "View3D > Sidebar > Delete Default Cube",
    "description": "Deletes the default cube with a button",
    "warning": "",
    "wiki_url": "",
    "category": "Object"
}

class DeleteDefaultCube(bpy.types.Operator):
    """Deletes the default cube with a button"""
    bl_idname = "object.delete_default_cube"
    bl_label = "Delete Default Cube"
    bl_options = {"REGISTER", "UNDO"}

    def execute(self, context):
        bpy.data.objects["Cube"].select_set(True)
        bpy.ops.object.delete()
        return {"FINISHED"}

class DeleteDefaultCubePanel(bpy.types.Panel):
    """Creates a panel in the 3D View sidebar"""
    bl_label = "Delete Default Cube"
    bl_idname = "OBJECT_PT_delete_default_cube"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"
    bl_category = "Delete Default Cube"

    def draw(self, context):
        layout = self.layout
        row = layout.row()
        row.operator("object.delete_default_cube")

def register():
    bpy.utils.register_class(DeleteDefaultCube)
    bpy.utils.register_class(DeleteDefaultCubePanel)

def unregister():
    bpy.utils.unregister_class(DeleteDefaultCube)
    bpy.utils.unregister_class(DeleteDefaultCubePanel)

if __name__ == "__main__":
    register()