Remove quick actions for milestone and iterations from Incidents

The following discussion from !40283 (merged) should be addressed:

• @engwan started a discussion: (+1 comment)

  Thanks @oregand, @splattael. backend looks good to me 👍

  We are planning to add backend changes to prevent setting of milestones / iterations in a separate MR right? And also the quick actions autocomplete removal? Just making sure we don't forget them.