Remove Promise type definition from beforeRemove event listener

[marciogurka]

Forum post

On the definition of the beforeRemove listener, we have the Promise<boolean> as a possible return, but that's not correct, so we need to fix that.
https://bryntum.com/products/grid/docs/api/Core/data/AjaxStore#event-beforeRemove

/**
     * Fired before records are removed from this store by the [remove](https://bryntum.com/products/scheduler/docs/api/Core/data/mixin/StoreCRUD#function-remove) or [removeAll](#Core/data/mixin/StoreCRUD#function-removeAll).
     * Also fired when removing a child record in a tree store using [removeChild](https://bryntum.com/products/scheduler/docs/api/Core/data/mixin/TreeNode#function-removeChild).
     * The remove may be vetoed by returning `false` from a handler.
     * @param {object} event Event object
     * @param {Store} event.source This Store
     * @param {Model[]} event.records The records which are to be removed.
     * @param {Model} event.parent The record from which children are being removed when using a tree store. Only provided when removing a single node.
     * @param {boolean} event.isMove This flag is `true` if the child node is being removed by [appendChild](https://bryntum.com/products/scheduler/docs/api/Core/data/mixin/TreeNode#function-appendChild) to be moved *within the same tree*.
     * @param {boolean} event.removingAll This flag is `true` if the operation is removing the store's entire data set.
     */
    beforeRemove?: ((event: { source: Store, records: Model[], parent: Model, isMove: boolean, removingAll: boolean }) => Promise<boolean>|boolean|void)|string
    ```