I didn't find it at all unnecessary. It established several things:
1] The Klingon presence in this universe [Kronos, Birds of Prey, et al].
2] The look and behavior of the Klingons in this universe [Forehead ridges, Klingon language, Warrior castes]
3] Uhura develops further character growth involving how she communicated and dealt with the Klingons.
And it sets up what may be a large storyline for the next movie.