Promotion adjustments not removed

[hendrik-advantitge]

Describe the bug
The applyOrderPromotions() method removes all adjustments on the different OrderItems prior to calculating new adjustments. If there were adjustments on the OrderItems before, but the new calculation does not generate any adjustments, the updatedItems array remains empty and no OrderItems are returned. As a consequence, the adjustments are not actually cleared from the Order.

To Reproduce
Steps to reproduce the behavior:

1. Create a promotion action, like this one here:

import { idsAreEqual,  LanguageCode,  Order,  PromotionOrderAction,  RequestContext } from '@vendure/core'
export const exampleAction = new PromotionOrderAction({
  code: 'example',
  description: [ { languageCode: LanguageCode.en, value: 'Buy { product_1 } get { product_2 } free' } ],
  args: { product_1: { type: 'ID' }, product_2: { type: 'ID' } },
  execute: async function (ctx: RequestContext, order: Order, { product_1, product_2 } ): Promise<number> {
    const productLine_1 = order.lines.find(line => idsAreEqual(line.productVariant.id, product_1))
    const productLine_2 = order.lines.find(line => idsAreEqual(line.productVariant.id, product_2))
    if (productLine_1 && productLine_2) {
      return -1 * Math.min(productLine_1.quantity, productLine_2.quantity) * productLine_2.unitPriceWithTax
    }
    return 0
  },
})

2. Create the promotion in the AdminUI, product_1 = 1, product_2 = 2
3. Add product 1 and product 2 to Order
4. A discount should be added
5. Remove product 2 from Order
6. The discount is still there

Expected behavior
The discount should no longer be applied.

Environment (please complete the following information):

• @vendure/core version: 0.18.4